Washington (CNN) - A key Democrat on the Senate Armed Services Committee said Wednesday that he will vote for a compromise plan to repeal the "don't ask, don't tell" policy that bans openly gay and lesbian soldiers from military service.
The endorsement from moderate Democratic Sen. Ben Nelson of Nebraska boosted the chances for the proposal to win committee support as soon as Thursday.
However, the leaders of the four branches of the military said Wednesday in letters to Republican Sen. John McCain and Rep. Buck McKeon that they opposed any congressional action on the policy now, before the military completes its review of the matter.
Read Marine Corps Commandant James T. Conway's letter here.
Read Chief of Staff of the United States Army George W. Casey's letter here.
Read Chief of Naval Operations Admiral Gary Roughead's letter here.
Read Air Force Chief of Staff General Norton A. Schwartz letter here.
The proposed agreement - reached Monday by the White House and top congressional Democrats - calls for a repeal of the controversial policy after completion of a military review expected by the end of 2010, followed by a review certification from President Barack Obama, Defense Secretary Robert Gates and Joint Chiefs of Staff Chairman Adm. Mike Mullen.
Initial votes on the proposal in the Senate Armed Services Committee and the full House could occur Thursday.
Gates gave lukewarm support for the plan on Tuesday, saying he preferred to complete the review before proceeding to the legislative repeal. The letters to McCain, R-Arizona, and McKeon, R-California, from the heads of the Army, Navy, Marines and Air Force specifically opposed legislative action now, saying it would undermine the faith that service members put in the review process.
"I believe it is important, a matter of keeping faith with those currently serving in the Armed Forces, that the Secretary of Defense commissioned review be completed before there is any legislation to repeal" the policy, wrote Gen. Norman A. Schwartz of the U.S. Air Force.
Pentagon spokesman Geoff Morrell said that Gates' statement on Tuesday "speaks for itself, and obviously, so do theirs," referring to the letters from the military leaders. However, Morrell said that Gates' position was firm on backing the compromise being pushed by the White House and leading Democrats.
Supporters of repealing the policy have been pressuring congressional Democrats to act now, fearing the party will lose its House or Senate majority in November's midterm election and be unable to pass the measure then.
Nelson said in a statement he was convinced that Gates supports the compromise agreement.
"I spoke to Secretary Gates and he advised that while he preferred waiting until the study is completed, he can live with this compromise," Nelson said in a statement Wednesday. He said the compromise "shows that Congress values the Pentagon's review that will include the advice and viewpoints from our men and women in uniform, from outside experts and from the American people about how to implement the repeal. It rests ultimate authority to make this change with our military leaders. I believe this is the right thing to do."
A spokesman for Sen. Joe Lieberman of Connecticut, one of the authors of the compromise, told CNN that backers of the measure were "increasingly confident" of its chances for committee approval.
"This could very well be a historic week in the United States Congress," said Lieberman spokesman Marshall Wittmann. Lieberman, an independent, sits with the Senate's Democratic caucus.
Supporters of the measure need 15 votes on the Armed Services Committee to pass it. They now have 14, according to a CNN count, including Nelson and moderate Republican Sen. Susan Collins of Maine. The intentions of two other Democrats - Sen. Robert Byrd of West Virginia and Sen. Evan Bayh of Indiana - remain undeclared, but party sources say Bayh might support the measure.
On the House side, McKeon, the ranking Republican on the House Armed Services Committee, said Tuesday that he opposed congressional action before the military had time to complete its review. So does Mississippi Democratic Rep. Gene Taylor, who said that attaching the repeal amendment to the defense policy bill expected on the floor Thursday could doom the measure.
Republicans will now likely vote as a bloc against the defense policy bill, which had bipartisan support in committee, Taylor told CNN. So will some liberal Democrats who traditionally oppose the measure to protest government policy on Iraq and Afghanistan, Taylor said.
Asked if he warned Democratic leaders about the situation, Taylor said: "Yes, for the members of the leadership who still speak to me, I've made it abundantly clear what an incredibly stupid idea this is."
But an aide to Pennsylvania Rep. Patrick Murphy, the Democrat tasked with rounding up votes for passage of the plan in the House, told CNN Tuesday that he is "confident he will have the votes."
The aide, who didn't want to be identified discussing internal deliberations, said Murphy already has 192 co-sponsors for the proposal. He
also asserted that "dozens" of other members have said they will back the proposal, which needs 217 votes to pass.
The "don't ask, don't tell" legislative repeal plan emerged late Monday from a meeting at the White House involving administration officials, gay rights groups and Pentagon officials, sources told CNN. There were also talks on Capitol Hill involving White House lawyers, Pentagon officials and staff from the offices of influential House and Senate Democrats including House Speaker Nancy Pelosi, the sources added.
Gates has said he supports eventually repealing the policy, but was also responsible for launching the extensive review of how best to make the change.
A senior U.S. military official with direct knowledge of the review process told CNN that the Joint Chiefs of Staff remain committed to taking the time to get views from troops.
That process is well under way, the official said, noting that a survey will go out shortly to about 70,000 troops and families to solicit their views. In addition, the official said, town hall meetings already have been held around the country and more are expected, while a website provides a place for troops to write in their views.
According to the official, changing the process now before completing the review could be harmful because some troops believe the whole repeal initiative is an effort to appease supporters of repealing the policy.
The military needs until the end of 2010 to figure out how to implement the repeal in terms of housing, medical and marriage benefits, as well as issues involving the reinstatement of gay soldiers previously discharged under the policy, the official said.
A major problem might be determining how to reconcile the repeal of "don't ask, don't tell" with federal law that defines marriage as between a man a woman, the official added.