WASHINGTON — Defense Secretary Robert Gates today gave lukewarm support to a new White House-backed plan for a vote in Congress to immediately repeal the law that bans gays from serving openly in the military.

Even though the plan would let Gates decide when to implement repeal of the “don’t ask, don’t tell” policy, he has said he would have preferred more time to study the issue before Congress acts.

Gates “continues to believe that ideally the DOD review should be completed before there is any legislation” changing the law, Pentagon press secretary Geoff Morrell said. Gates has previously said he didn’t want to change the policy until the study is finished in December.

The House was expected to vote as early as Thursday on repeal of the 1993 law, which prohibits the military from asking service members whether they are gay, bans homosexual activity and requires that gay troops not discuss their sexual orientation.

In a compromise worked out Monday between the White House and some Democrats, the Defense Department’s personnel policies wouldn’t have to change until the president, defense secretary and chairman of the Joint Chiefs of Staff agree that the military was ready.

Rep. Patrick Murphy, D-Pa., an Iraq war veteran, was expected to introduce the legislation as an amendment to a defense policy bill. Sen. Carl Levin, chairman of the Armed Services Committee, was expected to offer the bill in the Senate as part of the same defense policy bill.

The bill’s chances of passing Congress are unclear, as Republicans would oppose it and many Democrats say they aren’t sure.

Murphy said in an interview today that he and other lawmakers have been working the issue for months and were confident it could pass both the House and the Senate.

“We need to get this done, and we need to get it done now,” Murphy said. “We are moving forward.

Gates had asked Congress repeatedly to hold off until after Dec. 1, so he could have time to study the issue. He was backed by President Barack Obama.

The White House announced late Monday that it would support the bill because it wouldn’t go into effect until the military says it’s ready. Gates “can accept the language in the proposed amendment,” Morrell said.

The Obama administration’s tepid endorsement may not win over conservative Democrats, particularly those in the Senate who say they want to wait before moving to repeal.

Gay rights groups are urging quick congressional approval of the legislation.

“Without a repeal vote by Congress this year, the Pentagon’s hands are tied and the armed forces will be forced to continue adhering to the discriminatory ‘don’t ask, don’t tell’ law,” says Joe Solmonese, president of the Human Rights Campaign.