Obama's Top Counterterrorism Adviser Defends Drone Strikes WASHINGTON - The Obama administration on Monday offered its first extensive explanation of how American officials decide when to use drones to kill suspected terrorists - a tactic that the government often treats as a classified secret even though it is widely known around the world. "Yes, in full accordance with the law - and in order to prevent terrorist attacks on the United States and to save American lives - the United States government conducts targeted strikes against specific Al Qaeda terrorists, sometimes using remotely piloted aircraft, often referred to publicly as drones," John O. Brennan, President Obama's top counterterrorism adviser, said before the Woodrow Wilson International Center for Scholars. The use of armed drones to strike at suspected militants in places like Pakistan and Yemen has grown dramatically under the Obama administration, and the emergence of the new technology - which has sharply reduced the cost and risk of warfare to its operators, making it easier to engage in sporadic combat in far-flung regions - has led to growing concerns both about civilian casualties and about a future in which other countries also acquire drones. The United States government has been reluctant to talk openly about its use of drones, apparently in part because foreign governments that granted permission for strikes did so on the condition that the deals would remain secret. Defending drone strikes as "legal, ethical, and wise," Mr. Brennan said the president had directed officials to be more open about how they "carefully, deliberately and responsibly" decide to kill terrorism suspects - including what he described as "the rigorous standards and process of review to which we hold ourselves today when considering and authorizing strikes against a specific member of Al Qaeda outside the "hot" battlefield of Afghanistan." Merely being a member of Al Qaeda or one of its allies is not enough to be targeted, Mr. Brennan said, because that describes many thousands of people. Rather, policymakers approve the killing of only those who pose a particular threat, he said, like operational leaders who are planning attacks against United States interests, lower-level militants training for such an attack, and those who possess "unique operational skills that are being leveraged in a planned attack." Mr. Brennan also said the administration preferred capturing such suspects alive - usually by telling a foreign government where to arrest them - and would authorize a strike only if that was not feasible. "We only authorize a particular operation against a specific individual if we have a high degree of confidence that the individual being targeted is indeed the terrorist we are pursuing," he said. This is a very high bar. Of course, how we identify an individual naturally involves intelligence sources and methods, which I will not discuss. But Mr. Brennan sidestepped a question about the use of "signature strikes," in which drones are used to target unidentified people whose activities - such as presence at a training camp - suggest they probably are militants. He said he was speaking only of "targeted strikes against specific individuals." Mr. Brennan added, "We only authorize a strike if we have a high degree of confidence that innocent civilians will not be injured or killed, except in the rarest of circumstances." But he acknowledged "instances when - despite the extraordinary precautions we take - civilians have been accidentally injured, or worse, killed in these strikes. It is exceedingly rare, but it has happened. When it does, it pains us and we regret it deeply, as we do any time innocents are killed in war. The killing of civilians by drones has fueled anti-American sentiment, especially in Pakistan. The number of such deaths - especially in remote regions where it is difficult for neutral observers to investigate - has been hotly disputed. American officials have described such deaths as rare, while critics have said there are far more than the government acknowledges. Mr. Brennan said American citizens who join Al Qaeda may also be targeted - after extra internal review, but he did not mention the killing of at least three Americans in drone strikes in Yemen last year, including Anwar Al-Awlaki, a radical cleric. The Obama administration is fighting to avoid disclosing information related to the targeted killing operations under the Freedom of Information Act, including lawsuits filed by The New York Times and by the American Civil Liberties Union. Jameel Jaffer, a litigator with the A.C.L.U., called Mr. Brennan's statement "important," but said the administration should disclose "the memo that authorizes the extrajudicial killing of American terrorism suspects" and "the evidence it relied on to conclude that an American citizen, Anwar Al-Awlaki, could be killed without charge, trial, or judicial process of any kind." Mr. Brennan listed four organizations that the United States government now considered to be part of the war against Al Qaeda: the "core" Al Qaeda, whose leadership he described as "a shadow of its former self"; two of its affiliates in Yemen and in North and West Africa; and the Shabab militia in Somalia, although he described it as "in decline" and mainly focused on parochial concerns. He also said the United States was monitoring the emergence in Nigeria of the group Boko Haram, which "appears to be aligning itself with Al Qaeda's violent agenda," but he stopped short of calling it an "affiliate" of Al Qaeda.