Enlarge By Harry Hamburg, AP Sen. Joseph Lieberman, I-Conn., and Sen. Susan Collins, R-Maine. Enlarge By Chip Somodevilla/Getty Images Joint Chiefs of Staff Chairman Adm. Michael Mullen, left, testifies with U.S. Defense Secretary Robert Gates before the Senate Armed Services Committee about the military's "don't ask, don't tell" policy on Capitol Hill Dec. 2. PUBLIC OPINION PUBLIC OPINION From Truman to Obama, see each president's ratings with USA TODAY's approval tracker.

WASHINGTON  Republicans stopped an attempt in the Senate on Thursday to repeal a law that prohibits gays from serving openly in the military.

Supporters were unable to muster the 60 votes needed to move ahead with a bill that would have allowed repeal, falling short in a 57-40 vote.

Democrats blamed Republicans who had vowed to block any legislation, including defense spending, until a deal is reached on extending an array of tax cuts due to expire Jan. 1.

"There are a lot of people all over the world right now in our military that are scratching their head, thinking what in the world has happened," said Sen. Claire McCaskill, D-Mo., pointing to funding for military operations.

Republicans blasted Senate Majority Leader Harry Reid, D-Nev., for stepping away from negotiations with a handful of Republicans, including Sen. Susan Collins of Maine. She expressed support for the most controversial element of the defense spending bill, the provision that would repeal "don't ask, don't tell," a 1993 law signed by President Clinton.

"The majority leader just closed the door," said Sen. Lisa Murkowski, R-Alaska, who favored repeal. "He had a path forward, and he chose not to do it."

President Obama expressed disappointment that "yet another filibuster has prevented the Senate from moving forward" with defense spending.

POLITICS BLOG: More on the Senate vote

Reid agreed to back an effort by Sen. Joe Lieberman, I-Conn., to bring up the repeal this month as a stand-alone bill, separate from defense spending.

Congress is scheduled to return home for Christmas next week, so time is running out.

It has been 48 years since Congress failed to pass a military spending bill.

A Pentagon questionnaire issued this year found that 70% of military members who responded said allowing gays to serve openly would have positive, mixed or no impact on the nation's war-fighting ability.

However, the survey showed that up to 60% of the troops engaged in direct combat in Iraq and Afghanistan say allowing gays to serve openly would have a negative impact on their ability to fight.

Advocates of retaining "don't ask, don't tell," led by Sen. John McCain, R-Ariz., say abandoning the law would be too disruptive to the military while the nation is engaged in two wars.

Defense Secretary Robert Gates and Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, endorse repealing the law and said the military could adapt to the change with minor risk to fighting ability.

They said the Pentagon study makes it clear that troops opposed to allowing gays to serve openly often change their views with training, education and familiarity with working alongside gay troops.

Other top military leaders were divided over the issue. Gen. John Amos, Marine Corps commandant, testified last week that half of his Marines are either in combat, recently returned from the fighting or preparing to deploy and this was the wrong time for such a change. The Army chief of staff, Gen. George Casey, agreed, although he said he favors eventual revocation of the law.

The Air Force chief of staff, Gen. Norton Schwartz, urged that repeal be delayed until 2012. Both the chief of naval operations, Adm. Gary Roughead, and the Coast Guard commandant, Adm. Robert Papp, favor lifting the ban.