Senate Republicans have blocked legislation that would have repealed the military's policy of "don't ask, don't tell" and allowed gay troops to serve openly.
Democrats failed Thursday to cinch a procedural deal with Republicans in the waning days of the lame-duck session. The 57-40 test vote fell three votes short of the 60 needed to advance.
The future of repeal is murky, since the lame-duck Congress is only in session for a few more weeks.
Senate Majority Leader Harry Reid, D-Nev., forced today's vote because he said he was tired of Republicans playing games. "Discrimination has never served America well," he said, adding the policy known as "don't ask, don't tell" hurts morale.
The ban on gays in the military has been in place since 1993.
Defense Secretary Robert Gates and Joint Chiefs of Staff Chairman Mike Mullen both support repeal and have urged Congress to act before the federal courts do. Congressional action would essentially give the Pentagon more time to implement a new policy.
Repeal of the policy has been tied up in a larger bill to authorize Pentagon programs and to give U.S. troops a pay raise.
Sen. John McCain, the top Republican on the Armed Services Committee, has been blocking the repeal because of concerns about the impact on military readiness. He mounted a filibuster this summer and Democrats could not get the 60 votes needed to get past McCain and proceed with a debate.
The Pentagon issued a long-awaited report earlier this month saying overturning the ban on "don't ask, don't tell" might be disruptive at first but not create long-term problems.
While Gates supports repeal of the policy, there has been resistance from the top generals in the Army and the Marines. Army Chief of Staff Gen. George Casey said he would not go forward with repeal during wartime because it could be divisive.
Maine Sen. Susan Collins, a moderate Republican, has been working with Reid to overcome objections from McCain and others in her party. She supports repeal, but sided with McCain in September because the Pentagon report had not yet come out and lawmakers wanted to add amendments to the bill.
Collins had won a key concession from Reid to allow 15 amendments on the Pentagon measure, but appeared to be taken by surprise when Reid called today's vote.
One challenge is that 42 Republicans have signed a letter saying they will not vote on legislation until work is done on tax cuts and other economic measures.
© Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.