WASHINGTON The future of President Barack Obama's health care overhaul now rests largely with two blocs of swing Democrats in the House of Representatives - abortion opponents and fiscal conservatives - whose indecision signals the difficulties Speaker Nancy Pelosi faces in securing the votes to pass the bill.

With Republicans unified in their opposition, Democrats are drafting plans to try on their own to pass a bill based on one Obama unveiled before his bipartisan health forum Thursday. His measure hews closely to the one passed by the Senate in December but differs markedly from the one passed by the House.

That leaves Pelosi in the tough spot of trying to keep wavering members of her caucus on board, while persuading some who voted no to switch their votes to yes - all at a time when Democrats are worried about their prospects for re-election.

Rep. Dennis Cardoza, D-Calif., typifies the speaker's challenge. The husband of a family practice doctor, he is intimately familiar with the failings of the U.S. health care system. His wife "comes home every night," he said, "angry and frustrated at insurance companies denying people coverage they have paid for."

But as a member of the centrist Blue Dog Coalition, Cardoza is not convinced Obama's bill offers the right prescription. It lacks anti-abortion language he favors, and he does not think it goes far enough in cutting costs. So while he voted for the House version - "with serious reservations," he said - now the congressman is on the fence.

"I think we can do better," he said.

Rep. Frank Kratovil Jr., D-Md., is also unconvinced. He voted against the House bill in November on the grounds that it is too big and too costly - a view that some constituents in his Republican-leaning district share. In case he did not get the message, one of them hanged him in effigy this past summer outside his district office on Maryland's Eastern Shore.

"This system is broken; we have to do something," Kratovil said. "But my preference would be to do smaller things."

For the moment, there is no actual bill. The tentative plan calls for the both the House and the Senate to use a parliamentary device known as reconciliation to pass a compromise measure.

The tactic is intended to avoid a Republican filibuster, but in the Senate, Majority Leader Harry Reid of Nevada faces challenges if he tries to use it. Reid is having trouble persuading a majority of his caucus to go along.

In the House, lawmakers like Kratovil and Cardoza, and other swing Democrats like them, will come under increasing scrutiny from leadership as a vote draws near. Of the 219 Democrats who initially voted in favor of the House measure, roughly 40 did so in part because it contained the so-called Stupak amendment, intended to discourage insurers from covering abortion.

Some - notably Rep. Bart Stupak, the Michigan Democrat for whom the amendment is named - will almost certainly switch their yes votes to no because the new version being pushed by Obama would strip out the House bill's abortion restrictions in favor of Senate language that many of them consider unacceptable.

An additional 39, like Kratovil, are fiscal conservatives who voted no the first time around. Pelosi is hoping that she can get some to switch those no votes to yes in favor of Obama's less expensive measure.

But persuading Democrats who are already on record as opposing a health overhaul to go on record as in favor will not be easy, especially during a midterm election year in which Democrats' political prospects already look bleak.

Of the 39 Democrats who voted against the House measure, 31, including Kratovil, represent districts that were won in 2008 by Sen. John McCain of Arizona, Obama's Republican rival. Fourteen, including Kratovil, are freshmen, who are generally considered more politically vulnerable than more senior lawmakers.

"The concern among Democrats right now is that there are more yes votes reconsidering than no votes," said David Wasserman, who tracks House races for the nonpartisan Cook Political Report. "My sense is that for Democrats to pass this bill, they would have to convince several members who are already in serious jeopardy, even after voting no on the first health care bill, to put passage of the bill ahead of their own chances of being competitive in the fall."

Publicly, House Democratic leaders are trying to sound upbeat.

The House Democratic whip, Rep. James Clyburn, D-S.C., said earlier this week that he felt "pretty good" about the chances of passing Obama's bill. But the leadership has not yet started counting votes, and a senior House leadership aide, speaking on condition of anonymity, conceded that rounding them up won't be easy.

"It's going to be a heavy lift," this aide said, "but so have many other votes. In the last health care vote we really didn't have the majority until the afternoon, and this will probably be that way too. That's how these votes come together in the end."