WASHINGTON?US President Barack Obama on Thursday scrapped a planned trip to Asia in favor of making an 11th-hour drive to help steer his historic health care overhaul through a cliffhanger Sunday vote.

"We greatly regret the delay," White House spokesman Robert Gibbs told reporters, but "passage of health insurance reform is of paramount importance and the president is determined to see this battle through."

The 10-year plan aims to extend coverage to 32 million Americans who currently have none, bringing the world's richest country closer than ever to guaranteeing health insurance for all of its citizens, with 95 percent of Americans covered.

Obama has courted three dozen lawmakers by telephone or in person since Monday, Gibbs said, as his Democratic allies in the House of Representatives set the stage for the make-or-break test.

Democratic Senator Max Baucus, chairman of the Senate Finance Committee, praised Obama's ability to win over support for his top domestic priority, telling reporters: "His personal presence helps."

It was the second delay to Obama's trip to the Indonesia, Australia and the US territory of Guam.

He had originally been set to leave on Thursday, then put the trip off to Sunday and has now rescheduled it for June in order to throw his weight behind feverish efforts to corral the 216 votes needed to get the bill through the House.

"We feel very strong about where we are," said Democratic House Speaker Nancy Pelosi, but "every vote around here is a heavy lift."

In a huge boost for Democrats, the powerful AFL-CIO labor union declared its "strong, active support" behind the bill despite reservations about some of its contents, stressing: "We are convinced that now is the time to say "'Yes.'"

The president's Republican foes in Congress reasserted their united opposition and vowed to make every effort to derail what they called a costly and dangerous proposal.

"We're going to continue to work closely together to do everything that we can do to make sure that this bill never, ever, ever passes," said Republican House Minority Leader John Boehner.

Obama led Democrats in brandishing fresh figures from the independent Congressional Budget Office (CBO) showing the bill would cut the US budget deficit by $138 billion to 2019 and $1.2 trillion the following decade.

"This is but one virtue of a reform that will bring the accountability to the insurance industry and greater economic security to all Americans," said Obama, who hoped the figures would win over deficit-minded centrist Democrats.

The CBO said the plan would cost $940 billion over 10 years, roughly matching Obama's self-imposed trillion-dollar price tag, and would extend the solvency of the hugely popular government-run Medicare program for the elderly.

The bill, which would enact the most sweeping overhaul of US health care in four decades, aims to end abusive insurance company practices and curb soaring health care costs that already run double those of other rich countries.

A compromise between rival Senate and House versions passed last year, the package would create new insurance marketplaces starting in 2014 and require most Americans to carry insurance, while offering subsidies to many.

Some of its most popular measures include bans on insurers denying coverage because of preexisting illnesses, on insurers imposing lifetime caps on coverage and on insurers dropping people from coverage when they get sick.

Republicans, who opposed the plan from the start, condemned it as an unaffordable plan to foster undesirable government intrusion affecting one sixth of the US economy, with potentially disastrous results.

"This health care bill is bad for patients, it's bad for providers; our doctors, our nurses and our hospitals," and US taxpayers, said Republican Senator John Barrasso.

The United States is the only industrialized democracy that does not ensure universal health care coverage, with an estimated 36 million Americans uninsured.

House Democratic leaders have done little to deter talk that they will skirt a direct up-or-down vote on the unpopular Senate bill, planning instead to approve a package of "fixes" Sunday that would automatically "deem" the upper chamber's legislation to have been passed.

"They are going to continue to ram, ram, ram this bill through the Congress. Every kind of scheme known to man to try and get it through the Congress without a vote," said Boehner.

If the House approves the Senate bill and the fixes, the Senate, where Republicans have vowed to prevent an up-or-down vote, would take up the measure as early as Tuesday, under rules that blunt the minority party's ability to kill the bill with parliamentary delays.

If Republicans force changes to the bill, the House would have to vote again.