Prospects for a repeal of the military’s ban on openly gay service members remained very much in doubt Tuesday as Senate Democrats met resistance for the move on the Armed Services Committee and House Democrats faced defections of their own amid nearly unified Republican opposition.

Gay rights advocates and their allies were furiously whipping a deal brokered Monday by the White House that would attach the repeal of the “don’t ask, don’t tell” law to the defense authorization bill. House Democrats face a floor fight on the issue, perhaps later this week, while the Armed Services panel is gearing up for a pivotal vote on the issue Thursday.

Armed Services Chairman Carl Levin said Tuesday he still is not sure whether he has enough support to overturn the policy and will be talking to his colleagues heading into this week’s markup.

The Michigan Democrat said he would have preferred an outright repeal but said he would back the compromise brokered late Monday by the White House that won the qualified blessing of Defense Secretary Robert Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff.

That deal would tie the repeal to a certification from military brass and the president that ending the policy will not affect military readiness or morale. That certification would follow a review of the law expected by the end of the year.

Gates’ acceptance of the agreement should shore up the votes on Armed Services, Levin said, even though Gates made clear he would have preferred a delay in legislative action.

But no Republicans on the panel are expected to back the deal, and Democratic Sen. Jim Webb, a former Navy secretary, said he saw no reason to move ahead now.

“I support the process that we put in place in February, and I don’t think there’s any reason to pre-empt it,” the Virginia Senator said. “The White House and Secretary Gates both said they would prefer to have the study done before they move into legislation, and I support that.”

Other Senate Democrats on the committee appeared to be coalescing around the idea, however. Sen. Bill Nelson (Fla.) said he backs repeal; Sen. Evan Bayh (Ind.) seemed to be leaning that way as well.

“I think the policy needs to be changed. It’s just a question of when,” Bayh said. “They may have found an acceptable compromise.”

[IMGCAP(1)]In the House, several Blue Dog Democrats said they were still weighing their unease with the initial proposal against the compromise. Rep. Henry Cuellar (Texas), for example, said he has received a blunt directive from those serving on the Randolph Air Force Base in his district: “Don’t repeal, don’t repeal, don’t repeal.” But Cuellar said the go-ahead from Gates and Mullen is compelling him to rethink his position. “If they were not on board, it’d be hard to even consider it,” he said.

With only a handful of Republicans expected to back scrapping the ban, Democratic leadership will need to keep defections from their conservative wing in line to make the change. Rep. Patrick Murphy (D-Pa.), an Iraq War veteran leading the charge for repeal, has said repeatedly that Democrats have the votes they need.

But assuming Members adopt the amendment, the math gets even trickier on final passage of the defense authorization bill. Republican sources said they expect most of their ranks to vote against final passage if it includes the repeal. That could force Democratic leadership to pressure anti-war liberals inclined to oppose the defense measure to hold their noses and vote for it in the interest of turning back the ban.

“I think they’re going to have to do some work,” said Rep. George Miller (D-Calif.), a key ally of Speaker Nancy Pelosi (D-Calif.). Miller said he is not a “big fan” of the defense bill himself. “We’ll see,” he said. “I’m not going to let a legislative strategy be used to deny people basic human rights. So I guess it puts people like me in a tough position, but welcome to Washington.”

Likewise, Rep. Jim McGovern (D-Mass.), a leading liberal, said if leadership needs his vote on final passage, he would consider it. “Ending prejudice and bigotry in our armed forces is a big deal, and if we can accomplish that, it’s worth doing,” he said.

Last year’s defense authorization bill may offer a clue on the path forward for House leadership. The measure initially sailed through the chamber in June with wide bipartisan support, 389-22. But after Democrats added hate-crimes language in conference negotiations, scores of Republicans bolted. Still, Democrats managed to hold defections on their side down to 15 while hanging on to 44 Republicans, and the package passed comfortably, 281-146.

House Democratic leaders’ handle on the situation remained slippery on Tuesday as they focused their whip efforts on a heavier lift higher in the queue: passing a package extending tax breaks and unemployment benefits.

A Democratic leadership aide scoffed at the Republican claims of unity but said that whip efforts were continuing.

Levin, meanwhile, said there is very little risk that the “don’t ask, don’t tell” policy would be re-established under a future administration.

“We’ve already got the secretary of Defense and the chairman of the Joint Chiefs favoring ending the ban,” Levin said. And once it is repealed, the odds of reinstating it are “so remote it’s a little bit like whether or not we’re going to repeal the Civil Rights Act of 1964,” he said.