Washington (CNN) -- Defense Secretary Robert Gates issued a lukewarm endorsement Tuesday of a Democratic plan to repeal the military's "don't ask, don't tell" policy.
The proposed agreement -- reached Monday by the White House and top congressional Democrats -- calls for a repeal of the controversial policy to become final after completion of the military review expected by the end of 2010, followed by a review certification from President Obama, Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff.
Initial votes on the proposal in the Senate Armed Services Committee and the full House of Representatives could occur as soon as Thursday, sources have said.
Gates "continues to believe that ideally the [Defense Department] review should be completed before there is any legislation to repeal" the "don't ask, don't tell" law, according to a statement by Pentagon spokesman Geoff Morrell.
But "with Congress having indicated that is not possible, the secretary can accept the language in the proposed amendment."
Congressional Democratic sources said Monday they hoped Gates would explicitly support the compromise language because that could determine whether the measure will pass. Several Democrats in the Senate and House have said they would be reluctant to support any legislation that doesn't have the Pentagon's complete backing.
Rep. Howard "Buck" McKeon of California, the ranking Republican on the House Armed Services Committee, said Tuesday 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 bill, which had bipartisan support in committee, along with some liberal Democrats who traditionally oppose the defense measure to protest government policy on Iraq and Afghanistan, Taylor told CNN.
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 Rep. Patrick Murphy, D-Pennsylvania, who has the task of rounding up votes for passage of the plan in the House, said Tuesday that the lawmaker 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.
In the Senate Armed Services Committee, however, a source involved in vote counting said that Democratic leaders currently have 13 firm "yes" votes. Fifteen are required for passage. The source identified Sens. Robert Byrd of West Virginia, Ben Nelson of Nebraska and Evan Bayh of Indiana as Democratic holdouts.
One prominent GOP moderate on the committee, Sen. Scott Brown of Massachusetts, issued a statement Tuesday indicating his opposition to the Democratic plan.
"It would be premature to act on a repeal of the 'don't ask, don't tell' law at this time," Brown said. "I am keeping an open mind, but I do not support moving ahead until I am able to finish my review, the Pentagon completes its study, and we can be assured that a new policy can be implemented without jeopardizing the mission of our military."
The legislative plan to repeal "don't ask, don't tell" emerged late Monday from a meeting at the White House involving administration and Pentagon officials and gay rights groups, the sources said.
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, D-California, the sources added.
Gates has said he supports eventually repealing the policy, but he was also responsible for launching an extensive review of how best to make the change.
Sen. Carl Levin, D-Michigan, chairman of the Senate Armed Services Committee, recently said he would push for a measure to repeal the law immediately. Gates opposed the idea, saying in a letter to the House Armed Services Committee chairman that he "strongly opposed" any changes before completion of the military review.
Sen. Lindsey Graham of South Carolina, a top Republican on defense issues, also indicated his support for completion of the review before any possible repeal.
"I think most members really would like to hear from our commanders and men and women in uniform and get their input on a decision like this," said Graham, a member of the Senate Armed Services Committee.
A senior U.S. military official with direct knowledge of the review process said 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 their views.
The official noted that military commanders have been telling the troops for weeks that the review process was intended to ensure their views were incorporated in contingency planning in the event that Congress changes the law.
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.
An Obama administration letter released Monday night indicated the agreement would address those issues, saying its approach "recognizes the critical need to allow our military and their families the full opportunity to inform and shape the implementation process through a thorough understanding of their concerns, insights and suggestions."
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 and a woman, the official added.
Supporters of repealing the policy have been pressuring congressional Democrats to act now, fearing the party will lose its majorities in the House or Senate in November's midterm elections and be unable to pass the measure afterward.
A senior administration official said Monday it was the understanding at the White House that "Congress is determined to act this week."
CNN's Dana Bash, Tom Cohen, John King, Dan Lothian, Barbara Starr, Alan Silverleib and Deirdre Walsh contributed to this report.