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 necessary 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 last week. 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 American 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.

Some lawmakers 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 are fiscal conservatives who voted no the first time around. Pelosi is hoping 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 an easy task, especially during a midterm election year in which Democrats' political prospects already look bleak.