Senate Republicans dealt a severe and potentially fatal blow Tuesday to efforts this year to repeal the military's "don't ask, don't tell" policy, which bans gay men and women from serving openly in the armed forces.

Democrats were unable to sway a single Republican to begin debate on a defense authorization bill that included the repeal.

The failure to repeal the law, despite White House backing and majorities in Congress, marked a low point in the more than decade-long effort to rid a policy begun under President Bill Clinton. Democrats thought this was their best chance to undo the 17-year-old measure after President Obama had won the support of Defense Secretary Robert M. Gates and other military leaders to get rid of it.

But Republicans objected that Majority Leader Harry M. Reid (D-Nev.) had attached several politically motivated proposals to the measure.

Sen. John McCain (R-Ariz.), who led the charge against repeal, called Reid's plan a "blatant and cynical" political ploy aimed at galvanizing Democratic voters for the midterm elections.

The high-profile failure left some advocates of repeal feeling burned and blaming the White House and congressional Democrats for not acting sooner.

"The Democrats have been against 'don't ask, don't tell' for more than a decade and why we allowed this law to remain in effect for another two years is beyond me," said Richard Soccarides, who served as an adviser to Clinton on gay rights. "The Washington-based gay rights groups made a decision early on that they were better off going along with the president's timeline and that right now that looks like a serious miscalculation."

White House officials and Senate Democratic leaders said they hoped to revive the issue after the November elections, when they attempt once again the defense authorization bill.

White House press secretary Robert Gibbs told reporters that he did not think this was the "decisive moment" for the law's repeal and that the administration would "keep trying."

But the bill's fate after the election is murky, given the uncertainty of the outcome at the polls. If Republicans make major gains, it could be difficult for Democrats to push a contentious issue during an end-of-the-term lame-duck session.

A senior Republican Senate aide also said that although some GOP lawmakers don't necessarily oppose repeal, they don't want to act before a Pentagon review of the policy change has been completed. That deadline is Dec. 1, leaving little time before the end of the year to revive the issue.

Repeal advocates have pushed since the ban was put into effect in 1993, saying it unfairly discriminates against gays, who have to hide their sexual identity while serving in uniform, and keeps thousands of potential recruits from enlisting.