WASHINGTON -- A defiant President Obama sought Monday to revive his faltering plan to overhaul health care, delivering a full-throated promise to get comprehensive legislation and summoning lawmakers crucial to his effort to the White House. 

"Don't bet against us. We are going to make this thing happen," Obama told a news conference intended to focus on his nominee for surgeon general, Dr. Regina Benjamin. 

The appearance in the Rose Garden was the president's first public outing since his trip -- and the first after an up-and-down week in Congress. Consensus on his top domestic priority has proven elusive and the Democratic leadership's ambitious timetable for floor votes this summer has slipped. 

While the president was out of the country last week sizing up foreign leaders, rank-and-file lawmakers took a look at the emerging details of health care legislation and many decided they didn't like what they saw. They called a time out. In the House, conservative Democrats rebelled over costs. In the Senate, the Democratic leadership pulled the plug on a controversial financing scheme that a moderate Democrat worked out with Republican counterparts. 

Despite Obama's determination, there's no guarantee he'll succeed in the effort to get all Americans covered and try to better manage costs. 

With lawmakers concerned about costs above all else, Congress may decide to expand coverage slowly, phasing it in over a number of years. 

House Democrats expect to get moving again this week, and they may be able to muscle a bill through the floor by August, keeping to the schedule congressional leaders originally promised. 

In the Senate, it's going to take longer. 

House Speaker Nancy Pelosi, D-Calif., Majority Leader Steny Hoyer, D-Md., and Senate Majority Leader Harry Reid, D-Nev., were to meet with Obama at the White House on Monday afternoon, according to officials who spoke on condition of anonymity to discuss private deliberations. Joining the leaders at the session were Senate Finance Committee Chairman Max Baucus, D-Mont., and House Ways and Means Committee Chairman Charles Rangel, D-N.Y. 

Baucus and Rangel are in charge of the crucial job of coming up with how to pay for a comprehensive health care overhaul that would cost at least $1 trillion over 10 years, mostly for subsidies to help cover nearly 50 million uninsured Americans. But the two Democrats are taking very different routes. Rangel is shaping a bill that Democrats can support. Baucus is striving for a bipartisan compromise, which would have better chance of winning broad support, and which Obama says he wants. 

Obama lost no time signaling that he intends to be in the forefront of the action. 

"I just want to put everybody on notice, because there was a lot of chatter during the week that I was gone," the president said. "Inaction is not an option." 

Up to now, the president has avoided debating policy details, choosing instead to make the broader case for a health care overhaul, and leaving the day-to-day negotiations to his aides. Yet if Congress is getting stuck in a policy swamp, Obama may the only one who can get things moving again. He hinted as much on Monday: "Muscles in this town to bring about big changes are a little atrophied but we are whipping people back into shape," he said. 

A more direct role for the president would be fraught with political risks. He'd get the blame if the effort collapses. 

"The president's role is going to be critical, but it needs to be wielded very carefully and at exactly the right moment," said Drew Altman, president of the nonprofit Kaiser Family Foundation, a clearinghouse for health care information. "I think we're at a point where most of the heavy lifting still has to be done in Congress." 

Sen. Mike Enzi, R-Wyo., says that lawmakers agree on 80 percent of what should be done: Health care providers should be paid for the quality, not quantity, of services. All Americans should have access to health insurance. Government should help those who can't afford the premiums. Small businesses and self-employed people -- who now have the hardest time finding and keeping coverage -- need new ways to buy affordable insurance. 

But so far, issues that divide policymakers have dominated the debate. 

The four big ones: the overall cost of expanding coverage and how to pay for it, whether to create a government health insurance plan, requiring employers to contribute to workers' coverage, and the benefits tax that blew up the Senate plan -- but still retains some support. 

House Democrats have proposed raising income taxes on the wealthy. That appears to face opposition in the Senate, where a bipartisan group of senators is trying to reassemble a financing package now missing a key component: an unpopular tax on high-cost health insurance benefits, which would have raised $320 billion out of a $1 trillion package.