A Senate committee on Thursday took a first step toward ending the policy that allows gays to serve in the military only if they don't disclose their sexual orientation.
In a 16-12 vote, the Senate Armed Services Committee approved a provision to repeal the 1993 "don't ask, don't tell" policy.
Sen. Susan Collins of Maine, the only Republican to vote for the amendment to a defense spending bill, said it passed after "vigorous and aggressive debate."
Sen. Joe Lieberman, I-Conn., who promoted the measure with Armed Services Chairman Carl Levin, D-Mich., said: "It's time for this policy to go. It doesn't reflect America's best values of equal opportunity, and it's not good for the military."
Repealing the 1993 law, a priority of gay rights groups that President Barack Obama has pledged to pursue, still faces a tough road.
The full House is expected to take up the identical amendment late Thursday or Friday and opposition is fierce, particularly among Republicans who cited letters from military service chiefs urging Congress to hold off on the legislation until the Pentagon completes a study of the impact on military life and readiness.
The measure could face a filibuster when it reaches the Senate floor.
"I think it's really going to be very harmful to the morale and effectiveness of our military," said Sen. John McCain of Arizona, the top Republican on the Armed Services Committee and a leading opponent of the repeal.
Still, the vote was welcomed by gay rights groups. "This is the beginning of the end of a shameful ban on open service by lesbian and gay troops that has weakened our national security," said Joe Solmonese, president of Human Rights Campaign, a leading gay rights organization.
In the House, debate on "don't ask, don't tell" dominated an all-day session on a bill that approves more than $700 billion for military operations.
Democrats stressed that the measure was a compromise under which the repeal would not go into effect until the Pentagon completes its study, expected in December, and until Obama and military leaders certify that it would not adversely affect the military's ability to fight.
Republicans countered by reading similar letters written by the heads of the military services asking Congress to wait.
"I also believe that repealing the law before the completion of the review will be seen by the men and women of the Army as a reversal of our commitment to hear their views before moving forward," wrote Gen. George Casey, head of the Army.
Congress going first "is the equivalent to turning to our men and women in uniform and their families and saying, 'Your opinion, your view, do not count,'" said Rep. Howard "Buck" McKeon of California, the top Republican on the House Armed Services Committee.
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."
Rep. Patrick Murphy, a Pennsylvania Democrat who served in the Iraq war and who is the chief sponsor of the amendment, said, "We need to get this done, and we need to get it done now."
The Senate panel's vote of approval was sealed when Sen. Ben Nelson of Nebraska, a conservative Democrat, endorsed it earlier this week. He said then 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."
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.
The bill is H.R. 5136