JUSTICE STEVENS delivered the opinion of the Court.Since its enactment in 1968, the Federal Magistrates Act has permitted district courts to assign magistrates certain described powers and duties, as well as "such additional duties as are not inconsistent with the Constitution and laws of Page 490 U. S. 860 the United States." [Footnote 1]  The principal question presented is whether presiding at the selection of a jury in a felony trial without the defendant's consent is among those "additional duties."IPetitioners Jose Gomez and Diego Chavez-Tesina were among 11 persons named as defendants in a 21-count indictment alleging commission of multiple felonies, including conspiracy and racketeering, involving distribution of cocaine. [Footnote 2]  Having elected to stand trial, petitioners and three codefendants appeared before the Federal Magistrate to whom the District Judge had delegated the task of selecting a jury. [Footnote 3]  Defense counsel made timely objections to this assignment.  Following a telephone conversation with the District Judge, the Magistrate noted their objections and commenced voir dire.  App. 13-16.  As is the practice in the Eastern District of New York, the Magistrate, rather than the attorneys, posed questions to the venirepersons. [Footnote 4]  The Magistrate also introduced the prospective jurors to the offenses charged; instructed them on numerous points of law, including the presumption of innocence and the different burdens of persuasion in civil and criminal trials; and admonished chosen jurors not to discuss the case with anyone.  See generally Tr. of Jury Selection.  When defense counsel appeared before the Page 490 U. S. 861 District Judge eight days later, they renewed their objections to the Magistrate's role in jury selection.  The District Judge overruled the objections, but said he would review any of the Magistrate's rulings de novo.  App. 19.  Defendants registered no specific challenge to any juror, and trial proceeded; 10 days later, the jury returned guilty verdicts against all five defendants.  Gomez received two concurrent 10-year sentences, to be followed by a special 10-year parole term; Chavez-Tesina was ordered to serve 20 years on one count, with three lesser sentences to run concurrently, and lifetime special parole.On appeal, defendants made no special claim of prejudice.  They contended, as petitioners do before this Court, that the Magistrate had no power to conduct the voir dire examination and jury selection.  A divided panel of the Court of Appeals rejected this argument.  United States v. Garcia, 848 F.2d 1324 (CA2 1988).  The court held that Congress intended the additional duties clause to be construed broadly enough to include jury selection by magistrates.  Id. at 1329.  Such a designation, the majority added, does not violate Article III or the Due Process Clause of the Federal Constitution.  Id. at 1330-1333.  The dissenting judge expressed doubts concerning both the majority's statutory interpretation and its constitutional analysis, and concluded that the court should exercise its supervisory powers to forbid delegation of voir dire to magistrates "except, possibly, when the parties consent, and then only pursuant to rules controlling the district court's review." [Footnote 5]The Second Circuit's decision conflicts with the holding of the Fifth Circuit in United States v. Ford, 824 F.2d 1430, 1438 (1987) (en banc), cert. denied, 484 U. S. 1034 (1988).  The Government had urged the court to construe the additional Page 490 U. S. 862 duties clause of the Federal Magistrates Act to allow judges to delegate jury selection in felony trials even without the defendant's consent.  That construction would provoke "grave constitutional questions," the en banc majority stated. 824 F.2d  at 1430; see id. at 1435.  After stressing the importance of jury selection and noting the specificity with which Congress defined magistrates' duties regarding other judicial proceedings, the majority concluded:"Additional duty is a residuum, granting the power to delegate any task not otherwise forbidden after we carve away that congery of duties that Congress never envisioned would be delegated.  We are not persuaded that Congress intended to grant authority to judges to delegate to magistrates the authority to preside over felony trials and over activities integral to and intimately tied with trial. [Footnote 6]"We granted certiorari to resolve this important conflict.  488 U.S. 838 (1989). [Footnote 7] Page 490 U. S. 863IIThe Federal Magistrates Act provides that a "magistrate may be assigned such additional duties as are not inconsistent with the Constitution and laws of the United States."  28 U.S.C. § 636(b)(3).  Read literally and without reference to the context in which they appear, these words might encompass any assignment that is not explicitly prohibited by statute or by the Constitution.  The Act itself specifies some proscriptions: magistrates "may hold no other civil or military office or employment under the United States," § 631(c), nor"engage in the practice of law [or] any other business, occupation, or employment inconsistent with the expeditious, proper, and impartial performance of their duties as judicial officers,"§ 632(a).  The only legal constraint on many other assignments not expressly barred -- whether supervising repair of the courthouse electrical system or presiding at felony trials -- must be found, according to the literal reading, in the Constitution.  The panel majority below and the dissenters in Ford embraced this construction, [Footnote 8] despite abiding concerns regarding the constitutionality of delegating felony trial duties to magistrates. [Footnote 9] Page 490 U. S. 864It is our settled policy to avoid an interpretation of a federal statute that engenders constitutional issues if a reasonable alternative interpretation poses no constitutional question.  See, e.g., Commodity Futures Trading Comm'n v. Schor, 478 U. S. 833,  478 U. S. 841 (1986); United States v. Rumely, 345 U. S. 41,  345 U. S. 45 (1953); Crowell v. Benson, 285 U. S. 22,  285 U. S. 62 (1932).  In this case, such an alternative interpretation of the additional duties clause readily may be deduced from the context of the overall statutory scheme.  Cf. Massachusetts v. Morash, ante at  490 U. S. 115 ("[I]n expounding a statute, we [are] not . . . guided by a single sentence or member of a sentence, but look to the provisions of the whole law, and to its object and policy"') (quoting Pilot Life Insurance Co. v. Dedeaux, 481 U. S. 41,  481 U. S. 51 (1987); Richards v. United States, 369 U. S. 1,  369 U. S. 11 (1962)).  When a statute creates an office to which it assigns specific duties, those duties outline the attributes of the office.  Any additional duties performed pursuant to a general authorization in the statute reasonably should bear some relation to the specified duties.  Thus, in United States v. Raddatz, 447 U. S. 667,  447 U. S. 674-676 (1980); Mathews v. Weber, 423 U. S. 261 (1976); and Wingo v. Wedding, 418 U. S. 461 (1974), we interpreted the Federal Magistrates Act in light of its structure and purpose.In Mathews, we considered whether preliminary review, argument, and preparation of recommended decisions in Social Security benefits cases were among the "additional duties" that a magistrate could perform.  The Government opposed such referrals, arguing that Congress intended a magistrate to be a "supernotary,'" assuming only the district judge's "irksome, ministerial tasks," [Footnote 10] while the benefits Page 490 U. S. 865 claimant likened the magistrate to a "`para-judge'" with "a wide range of substantive judicial duties and advisory functions."  423 U.S. at  423 U. S. 268.  Declining to choose either extreme or to read the "additional duties" language literally, we examined the Act's structure and determined that limited, advisory review, subject to the district judge's ongoing supervision and final decision, fell among the "range of duties" that Congress intended magistrates to perform.  Id. at  423 U. S. 270.  In accordance with our reasoning in Mathews, our task is to consider the office of magistrate as it pertains to seating a jury in a felony case.IIIBefore 1968, minor federal legal disputes were settled by United States commissioners, who collected fees for their services and often were not lawyers.  Limitations on their jurisdiction resulted in the downgrading or dismissal of criminal offenses that otherwise would have to be tried by district judges.  H.R.Rep. No. 1629, 90th Cong., 2d Sess., p. 14 (1968).  The new office of magistrate, in contrast, was to be filled in most instances by attorneys.  82 Stat. 1108, 28 U.S.C. § 631(b) (1964 ed., Supp. IV).  Paid by salary, magistrates were to be appointed by district judges to definite terms from which they could be removed only for cause.  82 Stat. 1109, 28 U.S.C. §§ 631(e), (h).With enhanced status came greater responsibility.  The Act not only conferred upon magistrates all the powers that commissioners had enjoyed, § 636(a), but also permitted district courts to establish rules by which magistrates could be assigned"such additional duties as are not inconsistent with the"Constitution and laws of the United States.  The additional Page 490 U. S. 866 duties authorized by rule may include, but are not restricted to --"(1) service as a special master in an appropriate civil action, pursuant to the applicable provisions of this title and the Federal Rules of Civil Procedure for the United States district courts;""(2) assistance to a district judge in the conduct of pretrial or discovery proceedings in civil or criminal actions; and""(3) preliminary review of applications for post-trial relief made by individuals convicted of criminal offenses, and submission of a report and recommendations to facilitate the decision of the district judge having jurisdiction over the case as to whether there should be a hearing."§ 636(b).  Commissioners had tried only "petty offenses." [Footnote 11]  Magistrates were empowered to try "minor offenses," [Footnote 12] but only upon special designation by the district court and only if the defendant, in writing, specifically waived his or her rights to trial before a judge, and perhaps by a jury.  82 Stat. 1116, 18 U.S.C. § 3401(b) (1964 ed., Supp. IV).  A convicted defendant could appeal to the district court, § 3402, and Congress contemplated that district courts would retain "the greatest possible scrutiny and control of a magistrate's trial jurisdiction," H.R.Rep. No. 1629, at 21. [Footnote 13]  Exempted from that Page 490 U. S. 867 jurisdiction were a number of minor offenses -- such as bribery and public corruption, deprivation of rights under color of law, and jury tampering, 82 Stat. 1116, 18 U.S.C. § 3401(f) (1964 ed., Supp. IV) -- that required the exercise of delicate judgment and "as a matter of sound congressional policy, ought to be tried in the U.S. district courts."  H.R.Rep. No. 1629, at 22.In 1976, Congress amended the Act "to clarify and further define the additional duties which may be assigned to a United States Magistrate," [Footnote 14] H.R.Rep. No. 94-1609, p. 2 (1976). [Footnote 15]  Upon consent of the parties, a magistrate could be Page 490 U. S. 868 designated a special master in any civil case.  90 Stat. 2729, 28 U.S.C. § 636(b)(2) (1976 ed.).  A magistrate also could be assigned to "hear and determine any pretrial matter," [Footnote 16] subject to reconsideration by the district court on a showing that "the magistrate's order is clearly erroneous or contrary to law."  § 636(b)(1)(A).  Excepted were eight categories of "dispositive" pretrial motions; with regard to these, a magistrate might conduct evidentiary and other hearings and recommend Page 490 U. S. 869 dispositions.  § 636(b)(1)(B).  If a party objected to the magistrate's recommendation, the judge was to "make a de novo determination" of the matter.  § 636(b)(1)(C).  The 1968 Act had listed such functions among a magistrate's additional duties; the 1976 amendments, in contrast, first described specific duties and then stated in a separate subsection that a "magistrate may be assigned such additional duties as are not inconsistent with the Constitution and laws of the United States."  § 636(b)(3).  A Committee Report explained:"Under this subsection, the district courts would remain free to experiment in the assignment of other duties to magistrates which may not necessarily be included in the broad category of 'pretrial matters.'  This subsection would permit, for example, a magistrate to review default judgments, order the exoneration or forfeiture of bonds in criminal cases, and accept returns of jury verdicts where the trial judge is unavailable.  This subsection would also enable the court to delegate some of the more administrative functions to a magistrate, such as the appointment of attorneys in criminal cases and assistance in the preparation of plans to achieve prompt disposition of cases in the court.""If district judges are willing to experiment with the assignment to magistrates of other functions in aid of the business of the courts, there will be increased time available to judges for the careful and unhurried performance of their vital and traditional adjudicatory duties."H.R.Rep. No. 94-1609, at 12.By 1979, congressional concerns regarding magistrates' abilities had decreased; a legislative Committee reported that "the magistrate system now plays an integral and important role in the Federal judicial system." [Footnote 17]  H.R.Rep. No. 96287, p. 5 (1979).  Accordingly, in the Federal Magistrates Page 490 U. S. 870 Act of 1979, Pub.L. 96-82, 93 Stat. 643-647, Congress enlarged the magistrate's jurisdiction over civil and criminal trials, codifying some of the experiments conducted under the Act's additional duties clause.  See H.R.Rep. No. 96287, at 2, 17.  Thus, since 1979, magistrates have been authorized to preside at, and enter final judgment in, civil trials, including those tried before a jury.  93 Stat. 643-644, 28 U.S.C. § 636(c).  For the first time, magistrates were permitted to conduct jury, as well as bench, trials on any misdemeanor charge. [Footnote 18]  93 Stat. 646, 18 U.S.C. § 3401(b).  As before, however, a magistrate's trial jurisdiction can be exercised only upon special designation by the district court, 93 Stat. 643, 28 U.S.C. § 636(c)(1); 93 Stat. 645, 18 U.S.C. § 3401(a), and it remains subject to judicial review. [Footnote 19]A critical limitation on this expanded jurisdiction is consent.  As amended in 1979, the Act states that"neither the district judge nor the magistrate shall attempt to persuade or induce any party to consent to reference of any civil matter to a magistrate."93 Stat. 643, 28 U.S.C. § 636(c)(2).  In criminal cases, the Government may petition for trial before a district judge. [Footnote 20]  "Defendants charged with misdemeanors Page 490 U. S. 871 can refuse to consent to a magistrate, and thus effect the same removal," S.Rep. No. 96-74, p. 7 (1979), for the magistrate's criminal trial jurisdiction depends on the defendant's specific, written consent. [Footnote 21]IVThrough gradual congressional enlargement of magistrates' jurisdiction, the Federal Magistrates Act now expressly authorizes magistrates to preside at jury trials of all civil disputes and criminal misdemeanors, subject to special assignment, consent of the parties, and judicial review.  The Act further details magistrates' functions regarding pretrial and post-trial matters, specifying two levels of review depending on the scope and significance of the magistrate's decision.  The district court retains the power to assign to magistrates unspecified "additional duties," subject only to conditions or review that the court may choose to impose.  By a literal reading, this additional duties clause would permit magistrates Page 490 U. S. 872 to conduct felony trials.  But the carefully defined grant of authority to conduct trials of civil matters and of minor criminal cases should be construed as an implicit withholding of the authority to preside at a felony trial. [Footnote 22]  The legislative history, with its repeated statements that magistrates should handle subsidiary matters to enable district judges to concentrate on trying cases, [Footnote 23] and its assurances that magistrates' adjudicatory jurisdiction had been circumscribed in the interests of policy as well as constitutional constraints, [Footnote 24] confirms this inference.  Similar considerations lead us to conclude that Congress also did not contemplate inclusion of jury selection in felony trials among a magistrate's additional duties. [Footnote 25]Even though it is true that a criminal trial does not commence for purposes of the Double Jeopardy Clause until the jury is empaneled and sworn, Serfass v. United States, 420 Page 490 U. S. 873 U.S. 377,  420 U. S. 388 (1975), other constitutional rights attach before that point, see, e.g., Brewer v. Williams, 430 U. S. 387,  430 U. S. 398 (1977) (assistance of counsel).  Thus, in affirming voir dire as a critical stage of the criminal proceeding, during which the defendant has a constitutional right to be present, the Court wrote:  "[W]here the indictment is for a felony, the trial commences at least from the time when the work of empanelling the jury begins.'"  Lewis v. United States, 146 U. S. 370,  146 U. S. 374 (1892) (quoting Hopt v. Utah, 110 U. S. 574,  110 U. S. 578 (1884)).  See Swain v. Alabama, 380 U. S. 202,  380 U. S. 219 (1965) (voir dire "a necessary part of trial by jury"); see also Ricketts v. Adamson, 483 U. S. 1,  483 U. S. 3 (1987); United States v. Powell, 469 U. S. 57,  469 U. S. 66 (1984).  Jury selection is the primary means by which a court may enforce a defendant's right to be tried by a jury free from ethnic, racial, or political prejudice, Rosales-Lopez v. United States, 451 U. S. 182,  451 U. S. 188 (1981), Ham v. South Carolina, 409 U. S. 524 (1973), Dennis v. United States, 339 U. S. 162 (1950), or predisposition about the defendant's culpability, Irvin v. Dowd, 366 U. S. 717 (1961).  Indications that Congress likewise considers jury selection part of a felony trial may be gleaned, inter alia, from its passage in 1975 of the Speedy Trial Act, 18 U.S.C. § 3161 et seq. (1982 ed. and Supp. V), [Footnote 26] and its placement of rules pertaining to criminal petit juries in a chapter entitled "Trial."  See Fed.Rules Crim. Proc. 23, 24; cf. id. Rule 43(a) (requiring defendant's presence "at every stage of the trial including the empaneling of the jury").Even assuming that Congress did not consider voir dire to be part of trial, it is unlikely that it intended to allow a magistrate to conduct jury selection without procedural guidance or judicial review.  Significantly, when Congress clarified the magistrate's duties in 1976, it did not identify the selection of a jury as either a "dispositive" matter covered by Page 490 U. S. 874 § 636(b)(1)(B) or a "nondispositive" pretrial matter governed by § 636(b)(1)(A).  To the limited extent that it fits into either category, we believe jury selection is more akin to those precisely defined, "dispositive" matters for which subparagraph (B) meticulously sets forth a de novo review procedure. [Footnote 27]  It is incongruous to assume that Congress implicitly required such review for jury selection, yet failed even to mention that matter in the statute.  It is equally incongruous to assume, in the alternative, that Congress intended not to require any review -- not even the less stringent clearly erroneous standard applicable to other pretrial matters [Footnote 28] -- of a magistrate's selection of a jury.  Yet one of those assumptions would be a necessary component of a conclusion that Congress intended jury selection to be one of a magistrate's additional duties.In any event, we harbor serious doubts that a district judge could review this function meaningfully.  Far from an administrative empanelment process, voir dire represents jurors' first introduction to the substantive factual and legal issues in a case.  To detect prejudices, the examiner -- often, in the federal system, the court -- must elicit from prospective Page 490 U. S. 875 jurors candid answers about intimate details of their lives.  The court further must scrutinize not only spoken words but also gestures and attitudes of all participants to ensure the jury's impartiality.  See, e.g., Wainwright v. Witt, 469 U. S. 412,  469 U. S. 428, n. 9 (1985) (quoting Reynolds v. United States, 98 U. S. 145,  98 U. S. 156-157 (1879)).  But only words can be preserved for review; no transcript can recapture the atmosphere of the voir dire, which may persist throughout the trial. [Footnote 29]  Cf. Waller v. Georgia, 467 U. S. 39,  467 U. S. 49, n. 9 (1984) ("While the benefits of a public trial are frequently intangible, difficult to prove, or a matter of chance, the Framers plainly thought them nonetheless real").  The absence of a specific reference to jury selection in the statute, or indeed, in the legislative history, [Footnote 30] persuades us that Congress Page 490 U. S. 876 did not intend the additional duties clause to embrace this function.VThe Government concedes, as it must, that errors occurring during jury selection may be grounds for reversal of a conviction.  Brief for United States 44, n. 41 (citing Batson v. Kentucky, 476 U. S. 79,  476 U. S. 85 (1986); Witherspoon v. Illinois, 391 U. S. 510,  391 U. S. 522 (1968)).  Yet it argues that any error in these cases was harmless, because petitioners allege no specific prejudice as a result of the Magistrate's conducting the voir dire examination.  Brief for United States 42-45.  We find no merit to this argument.  Among those basic fair trial rights that "can never be treated as harmless'" is a defendant's "right to an impartial adjudicator, be it judge or jury."  Gray v. Mississippi, 481 U. S. 648,  481 U. S. 668 (1987) (quoting Chapman v. California, 386 U. S. 18,  386 U. S. 23 (1967)).  Equally basic is a defendant's right to have all critical stages of a criminal trial conducted by a person with jurisdiction to preside.  Thus, harmless error analysis does not apply in a felony case in which, despite the defendant's objection and without any meaningful review by a district judge, an officer exceeds his jurisdiction by selecting a jury.The judgment of the Court of Appeals isReversed
U.S. Supreme CourtGomez v. United States, 490 U.S. 858 (1989)Gomez v. United StatesNo. 88-5014Argued April 24, 1989Decided June 12, 1989*490 U.S. 858SyllabusA Magistrate assigned by the District Judge conducted the voir dire examination and jury selection for petitioners' trial on multiple felony counts.  The judge overruled petitioners' objections to the assignment of the Magistrate.  The judge offered to review any of the Magistrate's rulings de novo, but petitioners registered no specific challenge to the selection of any juror.  After petitioners were convicted and sentenced, they contended on appeal that the Magistrate had no power to conduct the voir dire examination and jury selection, but made no specific claim of prejudice.  The Court of Appeals affirmed their convictions, noting that the Federal Magistrates Act permits district courts to assign magistrates certain described powers and duties, as well as "such additional duties as are not inconsistent with the Constitution and laws of the United States."  The court held that Congress intended this additional duties clause to be construed broadly enough to include jury selection by magistrates, adding that such a designation does not violate Article III or the Due Process Clause.Held:1. Presiding at the selection of a jury in a felony trial without the defendant's consent is not one of the "additional duties" that the Act permits courts to assign to magistrates.  Pp.  490 U. S. 863-876.(a) Read literally and without reference to its statutory context, the additional duties clause encompasses any assignment that is not explicitly prohibited by statute or by the Constitution.  It is the Court's settled policy, however, to avoid an interpretation of a federal statute that engenders constitutional issues if a reasonable alternative interpretation poses no constitutional question.  Thus it is appropriate to examine the Act's overall structure and purpose to determine whether any "additional duties" assigned to a magistrate bear some reasonable relation to the other duties that, because they are specifically enumerated in the Act, define the attributes of the magistrate's office.  See, e.g., Mathews v. Weber, 423 U. S. 261.  Pp.  490 U. S. 863-865.(b) The Act's structure and legislative history demonstrate a congressional intent to limit a magistrate's range of duties in criminal cases Page 490 U. S. 859 to:  performing certain pretrial and post-trial functions, subject to one of two levels of judicial review depending on the scope and significance of the magistrate's decision; and conducting bench and jury trials on misdemeanor charges, but only upon special assignment by, and subject to the review of, the district court, and only with the consent of the parties.  Pp.  490 U. S. 865-871.(c) The absence of a specific reference in the Act or its legislative history to jury selection in felony trials demonstrates that Congress did not intend the additional duties clause to embrace this function.  Voir dire in a felony case is a critical stage of the trial.  However, the Act's carefully defined grant of authority to magistrates to conduct trials of minor criminal cases must be construed as an explicit withholding of the authority to preside at felony trials.  Even assuming that Congress did not consider voir dire to be part of the trial, it is unlikely that it intended to allow a magistrate to conduct jury selection as an "additional duty" not subject to the procedural guidance or judicial review applicable to pretrial matters.  In any event, it is doubtful that a district judge could review the jury selection function meaningfully, since no transcript can recapture the atmosphere of the voir dire.  Pp.  490 U. S. 871-876.2. There is no merit to the Government's argument that any error was harmless because petitioners allege no specific prejudice as a result of the Magistrate's conducting the voir dire.  Harmless error analysis does not apply in a felony case in which, despite the defendant's objection and without any meaningful review by a district judge, an officer exceeds his jurisdiction by selecting a jury.  P.  490 U. S. 876.848 F.2d 1324, reversed.STEVENS, J., delivered the opinion for a unanimous Court.