President Barack Obama's Democratic allies have pushed the most sweeping US health care overhaul in a half-century through the House of Representatives but the measure's future is far from clear.
On Saturday the representatives voted 220-215 for the bill, which is estimated to cost $US1 trillion ($A1.1 trillion) over 10 years and extend health coverage to about 36 million Americans who now go without it
But the outlook for Senate action is cloudy and both chambers must pass identical legislation to send it to Obama to sign his top domestic priority into law.
"Now the United States Senate must follow suit and pass its version of the legislation. I am absolutely confident it will and I look forward to signing comprehensive health insurance reform into law by the end of the year," Obama said in a statement after the House vote.
A typical path would be for the Senate to approve its version of the legislation, then for the two chambers to thrash out their differences and agree on a compromise measure in a process called a "conference."
However Democratic Senate Majority Leader Harry Reid signalled after closed-door talks with his party this week that intra-party divisions mean passing a bill this year may not happen.
"We're not going to be bound by any timelines. We need to do the best job we can for the American people," said Reid, who needs 60 votes to ensure the ability to overcome parliamentary delaying tactics and pass a bill.
Democrats control 58 seats and can reach the 60-vote threshold with the support of the chambers two independents - but some moderates are baulking and one of the independents has openly opposed the plan as written.
As in the House, all but one Republican united against the White-House backed provision and Senate Democrats are divided on key issues like the government's role in any revamped health care system.
Pushing the fight to 2010 could complicate the delicate coalition-building needed to pass the bill because it is a midterm election year, when the entire House and one third of the Senate are up for reelection.
Reid spokesman Jim Manley later stuck to the hoped-for 2009 completion goal, saying: "There is no reason why we can't have a transparent and thorough debate in the Senate and still send a bill to the president by Christmas."
