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WASHINGTON -- Congress neared precedent-setting votes Thursday on whether to allow gays to serve openly in the military.

A House vote, which could come Thursday evening, would repeal the 1993 law known as "don't ask, don't tell" that has effectively required gays wishing to join the military to hide their sexual orientation.

The Senate Armed Services Committee was also prepared to vote on the issue. In both cases the initiative to end the ban was attached to a $760 billion defense spending bill.

The gay rights amendment, supported by President Obama, is the product of a compromise with Pentagon leaders: It will not go into effect until the Pentagon completes a study, expected in December, on the ramifications of the policy change and until the president, the defense secretary and chairman of the Joint Chiefs of Staff certify that it won't hurt the military's ability to fight.

As debate on the defense bill opened in the House, Republicans objected to legislating the ban before the study is completed.

"We're saying 'we're shoving this down your throat,"' said Rep. Louis Gohmert, R-Texas. "The military is not a social experiment. We are sending them out there with a mission to protect this country."

But Rep. Jared Polis, an openly gay Democrat from Colorado, said most Americans "recognize that on the battlefield, it doesn't matter if a soldier is lesbian, gay or straight. What matters is they get the job done for our country."

"We need to get this done, and we need to get it done now," said Rep. Patrick Murphy, a Pennsylvania Democrat who served in the Iraq war and who is the chief sponsor of the amendment.

Supporters said this week the Senate panel had enough votes to pass the bill after key holdouts, including Sen. Ben Nelson, a Nebraska Democrat, announced they would swing behind it.

"In a military which values honesty and integrity, this policy encourages deceit," Nelson said.

Nelson said a provision in the bill giving the military the power to decide on the details of implementing the policy was key to his support because it "removes politics from the process" and ensures repeal is "consistent with military readiness and effectiveness."

Sen. Robert Byrd, D-W.Va., another uncertain vote, also said Wednesday he would support the measure after succeeding in adding a provision that Congress will have 60 days to study the Pentagon study before the repeal goes into effect.

Advocates hoped the momentum in the Senate would carry over to the House, where several conservative Democrats -- including Rep. Gene Taylor of Mississippi -- threatened to oppose the massive defense spending bill if it included the repeal provision.

Defense Secretary Robert Gates has said he supports repeal but would prefer that Congress wait to vote until he can talk to the troops and chart a path forward. A study he ordered is due Dec. 1.

"With Congress having indicated that is not possible, the secretary can accept the language in the proposed amendment," said Pentagon press secretary Geoff Morrell.

The service chiefs this week urged the Senate panel not to vote until the Pentagon could complete its survey of military personnel.

"The value of surveying the thoughts of Marines and their families is that it signals to my Marines that their opinions matter," Marine Commandant James Conway wrote in a letter to Sen. John McCain of Arizona, the panel's top Republican.

Adm. Mike Mullen, the nation's top uniformed officer and chairman of the Joint Chiefs of Staff, told graduating Air Force Academy cadets on Wednesday that they need to support a changing military.

Mullen didn't speak directly about the "don't ask, don't tell" policy. But the chairman, who has said that the policy unfairly forces troops to lie, said service members should question convention.

"Few things are more important to an organization than people who have the moral courage to question the direction in which the organization is headed and then the strength of character to support whatever final decisions are made," Mullen said.

The "don't ask, don't tell" policy, itself a compromise worked out during the Clinton administration, states that military leaders will not investigate a service member's sexual orientation as long as the member does not openly acknowledge that he or she is gay or engage in same-sex relations.

Some 14,000 people have been forced out of the military since then because of their sexual orientation.