WASHINGTON — Despite Democratic efforts, Republicans on Thursday prevented a vote on the "don't ask, don't tell" policy, putting the repeal of a ban on gays serving openly in the military in doubt.

Senate Democrats had been working to reach an agreement with Republicans to allow time to debate the broader defense authorization bill that would include the repeal of the ban. Republicans have vowed to block any votes until after resolving the unrelated issue of expiring tax cuts.

Nonetheless, Senate Majority Leader Harry Reid on Thursday called for the vote that included an offer of limited debate on the authorization bill. The vote was 57-40, short of the 60 votes needed to advance the bill for consideration.

With one week remaining until the scheduled end of this Congress, it is unclear whether lawmakers who have spent months pushing to end the ban will be able to revisit the issue.

A chief sponsor of repealing the ban on gays in the military, Sen. Joseph Lieberman (I-Conn.) has said the Senate should remain in session through the Christmas holiday season to pass the bill, which he calls the civil-rights issue of this era.

Failing to repeal "don't ask, don't tell" before Congress adjourns would be a blow to a top Obama administration priority and end the effort for the foreseeable future. When the new Congress convenes in January, the effort would face opposition from an emboldened GOP in both the House and Senate.

Some Republicans do support a repeal of the "don't ask, don't tell" policy but objected to how Democrats proceeded in bringing the legislation to the floor.

Speaking at the White House on Thursday, press secretary Robert Gibbs urged lawmakers to act.

"The president strongly believes that one of two things is going to happen. Either Congress is going to solve this legislatively, or the courts are going to decide this," he said. "Congress has to ask themselves how they want to end it and what role they want to play in ensuring that it's done in an orderly way."

A Pentagon report has said that repealing the ban that had been installed during the Clinton administration would not substantially disrupt the military, even during wartime as troops are engaged in Afghanistan.

In the report, a majority of service members said they would not object to serving with gay troops, though the Marine commandant has expressed concerns about repealing the ban while troops are engaged in combat.

lmascaro@tribune.com