Washington (CNN) -- Secretary of Defense Robert Gates issued a lukewarm endorsement Tuesday of a newly unveiled 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 a military review expected by the end of 2010, followed by a review certification from President Barack Obama, 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 as soon as Thursday, sources have told CNN.
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 told CNN on 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 are reluctant to support any legislation that doesn't have complete backing of the Pentagon.
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 Pennsylvania Rep. Patrick Murphy, the Democrat tasked with rounding up votes for passage of the plan in the House, told CNN Tuesday that Murphy 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 told CNN that Democratic leaders currently only have 13 firm "yes" votes. Fifteen are required for passage. The source identified West Virginia's Robert Byrd, Nebraska's Ben Nelson and Indiana's Evan Bayh as Democratic holdouts.
One prominent GOP moderate on the committee, Massachusetts Sen. Scott Brown, 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 "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 noted. 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.
Michigan Sen. Carl Levin, the Democratic 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.
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.
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.
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.
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 a woman, the official added.
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.
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, Alan Silverleib, Tom Cohen, John King, Barbara Starr, Dan Lothian, and Deirdre Walsh contributed to this report.