A last-ditch effort to scrap the military's controversial ban on gays and lesbians serving openly failed today after several moderate Republicans whose votes were considered crucial voted against repealing the "don't ask don't tell" policy.
President Obama said he was "extremely disappointed" that the bill failed.
The "don't ask, don't tell" law "weakens our national security, diminishes our military readiness and violates fundamental American principles of fairness, integrity and equality," the president said in a written statement. "While today's vote was disappointing, it must not be the end of our efforts. I urge the Senate to revisit these important issues during the lame duck session."
It came as a surprise when Senate Majority Leader Harry Reid, D-Nev., today abruptly called a procedural vote on the annual Defense Authorization bill that included a repeal of the "don't ask, don't tell" policy.
"There is simply no evidence and no justification -- legal, military or otherwise -- for keeping this policy in place," Reid said on the Senate floor, emphasizing that "it would be unconscionable to leave here without passing it."
For the past few days, Reid had been locked in negotiations with Sen. Susan Collins of Maine, a moderate Republican who supports the repeal but said she might vote against the bill on procedural grounds.
After a floor speech today in which she said she was "perplexed and frustrated" by Reid's decision to call a vote this afternoon, it was expected that she would vote against the repeal, but she ultimately backed the effort.
However, Sen. Lisa Murkowski, R-Alaska -- who originally said she would vote for repeal -- voted no. Other moderate Republican senators, including Olympia Snowe, R-Maine and Scott Brown, R-Mass., also voted no, along with a majority of Senate Republicans. Democratic Sen. Joe Manchin of West Virginia also voted against repeal.
The bill needed 60 votes to advance, but it received only 57.
On the legal front, the Obama administration is preparing legal briefs in support of "don't ask don't tell" and continues to argue that it does not want the repeal to come from the courts. The briefs, which challenge a lower court's finding that the policy is unconstitutional, are due by Jan. 24.
Collins and Sen. Joe Lieberman, an independent from Connecticut who caucuses with Democrats, said after the vote that they now will introduce free-standing legislation -- separate from the annual defense authorization bill -- to repeal the "don't ask, don't tell" policy.
"Sixty -- and I think maybe more than 60 members of the United States Senate -- have made clear that they support the repeal of 'don't ask don't tell,' and while that is the case, and it is the case, we are not going to give up," Lieberman said.
Lieberman said Reid has asked to co-sponsor the free-standing bill to repeal the policy and has promised to put it on an already-packed lame-duck calendar.
Passing the measure at this point will be far from easy because lawmakers already have a long to-do list for a short time frame. But both Lieberman and Collins argued that they have enough votes.
Collins, sticking with the GOP's line that the Senate first should resolve the issues of the Bush tax cuts and government funding before proceeding to any other matters, said the stand-alone bill can pass if it is brought to the floor at the right time.
"As long as the priority items -- taxes and funding -- have been completed, I believe that the votes are there," Collins said.
Both she and Lieberman ripped Reid for holding today's vote, saying they were "disappointed" in him.
"There was a clear path forward to victory on this issue and to consideration of this bill, and for the life of me I cannot understand why the majority leader chose not to take it," said Collins.
It will be far from easy with such a full slate of issues to resolve, but despite today's setback, a stand-alone repeal of "don't ask, don't tell" still could happen before year's end.
If a free-standing bill were to pass the Senate, it still would have to pass the House of Representatives, which could be a challenge because Republicans will gain control of the House next month.
The debate and vote on gays in the military is competing for time on the Senate schedule for the remainder of a lame-duck session that is expected to include addressing the Bush tax cuts, government funding and the START treaty with Russia.
Complicating matters further was Senate Republicans' stated refusal earlier this month not to vote for any measures until taxes and funding are resolved, a move denounced by Reid as merely an "artificial roadblock" designed to obstruct Democratic efforts.
"Putting up these artificial roadblocks is foolishness," Reid said. "What in the world do they accomplish by saying we're not going to allow you to do the START treaty, the defense authorization bill, until the tax bill is complete and spending is done?"
Today's vote marked the second time this year that lawmakers in the upper chamber have acted on the controversial issue.
On Sept. 21, Senate Republicans, led by Sen. John McCain, R-Ariz., shot down the bill. Democrats needed 60 votes to advance the bill over a GOP filibuster, but only secured 56 votes.
However, one of the no votes was from Reid, who only took that vote in a procedural move to allow him to bring up the measure again at a later date. Another one of those no votes was from Sen. Mark Pryor, D-Ariz., who announced Wednesday that he would now support the effort to change the policy.
"I have now carefully reviewed all of the findings, reports and testimony from our armed forces on this matter and I accept the Pentagon's recommendations to repeal 'don't ask, don't tell,'" Pryor said. "I also accept the secretary of defense and chairman of the Joint Chiefs' commitment that this policy can be implemented in a manner that does not harm our military's readiness, recruitment, or retention."
The controversial policy that prohibits gays serving openly in the military has been in effect since 1993. The House already has approved a conditional repeal of it, leaving its fate in the hands of the Senate.
ABC News' Huma Khan and Ariane de Vogue contributed to this report.