3 Democrats Say They Will Oppose Summers for Fed Lawrence H. Summers's prospects of becoming chairman of the Federal Reserve have become murkier since three key Democratic senators signaled in recent days that they would oppose his nomination. Senator Jon Tester, Democrat of Montana and a member of the Banking Committee, said on Friday that he would vote against sending Mr. Summers's nomination to the full Senate for a confirmation vote. Two of Mr. Tester's fellow Democrats on the committee, Senators Jeff Merkley of Oregon and Sherrod Brown of Ohio, have also signaled through their aides that they would vote no. Such resistance complicates matters for Mr. Summers because without the votes of those three Democrats, he would need Republican support on the Banking Committee, where Democrats have a three-vote majority. The panel holds the first vote on any nominee to lead the Fed. It is not clear how the rest of the committee might vote. Senator Elizabeth Warren, Democrat of Massachusetts, is believed to be reluctant to support Mr. Summers but has not said publicly how she would vote. President Obama is believed to prefer Mr. Summers, Treasury secretary in the Clinton administration and an Obama economic adviser, to succeed the current Fed chairman, Ben S. Bernanke, who is expected to step down at the end of January. It is unusual for senators to voice opposition to a nomination before the White House has even submitted it to the Senate. As skepticism grows among members of the president's own party, the White House has made it clear to Democrats on Capitol Hill that Mr. Summers is Mr. Obama's choice. Republicans, too, are wary of Mr. Summers. Senator John Cornyn of Texas, the No. 2 Senate Republican, and Senator Pat Roberts of Kansas have both said that they would not vote for Mr. Summers. In August, Mr. Roberts said, "I wouldn't want Larry Summers to mow my yard." Mr. Summers, who was also the president of Harvard, has attracted resistance for a variety of reasons, among them his comments about the aptitude of women in math and science. Senators like Mr. Tester also say that Mr. Summers has too often promoted the interests of large financial institutions over those of small community banks.