WASHINGTON — President Obama's yearlong quest to fix the nation's health care system faces its most critical test Sunday when House Democrats hope to pass a revised 10-year, $940 billion package expanding coverage to 32 million people.

Democrats plowed fresh billions into insurance subsidies for consumers yesterday and added a $250 rebate for seniors facing high prescription drugs.

Obama scuttled an Asian trip in favor of last-minute lobbying at the White House on his signature issue, playing host to a procession of wavering Democrats seeking favors.

"The president is determined to see this battle through," spokesman Robert Gibbs said.

The health care portions of the bill would affect nearly every American and remake one-sixth of the national economy.

Beginning in 2014, most Americans would be required for the first time to purchase insurance, and face penalties if they refused. Millions of families with incomes up to $88,000 a year would receive government help to defray their costs. Large businesses would face fines if they did not offer good-quality coverage to their workers.

"It will make history and we will make progress by passing this legislation," predicted House Speaker Nancy Pelosi as Democrats unveiled the final alterations to the bill meant to expand health care, bar the insurance industry from denying coverage on the basis of pre-existing medical conditions and trim federal deficits by an estimated $138 billion over the next decade.

As Democrats trumpeted their bill, particularly its potential impact on the deficit, Republicans attacked it relentlessly as a government takeover of the health care industry financed by ever higher Medicare cuts and tax increases, including a new Medicare payroll tax on upper-income wage earners.

Senate GOP leader Mitch McConnell said the new package includes $150 billion in additional tax increases and $60 billion in new Medicare cuts, according to a USA Today report.

"I would suggest that the president not scrap his trip to Indonesia," he said. "He should scrap this bill."

The health bill also provides an additional $8.5 billion over the next decade for 11 states, including Hawai'i, and the District of Columbia, to help them pay for the more generous Medicaid assistance they have been providing low-income residents.

The other 10 states are Arizona, Delaware, Maine, Massachusetts, Minnesota, New York, Pennsylvania, Vermont, Washington and Wisconsin.

SOME REVISIONS

House Democrats plan to approve the Senate version of the bill, which was passed Christmas Eve, along with a package of revisions designed to address some of the objections that they have to the bill. The Senate would then need to approve the revisions, which will come to the floor next week.

The revisions will come to the Senate in the form of a budget reconciliation bill, which cannot be filibustered, meaning it can be enacted with 51 Senate votes. Democrats control 59.

But budget reconciliation bills are subject to parliamentary points of order, any of which could stop the legislation in its tracks. Republicans said yesterday they have plenty of objections teed up.

"We have a responsibility to ensure that the rules of the Senate are not abused," said Sen. Lamar Alexander, of Tennessee, the No. 3 Senate GOP leader.

Another tactic Republicans could try: offering a potentially limitless series of amendments to the bill, any one of which would require its return to the House for what could become an endless game of legislative ping-pong.

"We're going to review it sentence by sentence," Alexander said.

As the House Democrats' Sunday showdown nears. support for the legislation appeared to be growing.

Rep. Bart Gordon of Tennessee, a moderate Demo-crat who is retiring at the end of the year, announced he would vote in favor of the bill after opposing an earlier version. He did so as Democratic leaders included in their revisions a provision worth an estimated $99 million over two years in higher Medicaid payments to Tennessee hospitals that treat large numbers of uninsured.

Rep. Betsy Markey, a first-termer from Colorado, quickly followed, citing improved deficit cuts.

That made three conversions in recent days, following liberal Rep. Dennis Kucinich of Ohio, with the White House and congressional leaders in search of more.

Rep. Luis Gutierrez of Illinois said he agreed to vote for the health care overhaul on the understanding that Obama and congressional Democrats would begin attempts quickly to pass comprehensive immigration legislation.

Obama and Democratic leaders focused their lobbying on two groups of Democrats, 37 who voted against an earlier bill in the House and 40 who voted for it only after first making sure it would include strict abortion limits that now have been modified.

After weeks of secrecy-shrouded meetings, Demo-crats unveiled 153 pages of last-minute changes that included another of Obama's top priorities. Federally guaranteed student loans would now be made only by the government, ending a role for banks and other for-profit lenders who charge fees.

The savings, an estimated $60 billion over a decade, would increase the maximum Pell grants for needy college students as well as support for programs such as aid to historically black colleges, a priority of the Congressional Black Caucus.

SUBSIDIES RAISED

As for health care, the additions fell generally into three categories.

• To address concerns of House Democrats, subsidies were raised by an estimated $25 billion over a decade for consumers who would face a first-ever requirement to purchase coverage.

• To ease concerns among governors, about $8 billion was added for 11 states and the District of Columbia, which already provide the level of Medicaid coverage that is required under the bill.

• Seniors who experience a gap in coverage in the Medicare prescription drug program would receive a $250 rebate this year — an election-year bragging point for Democrats as they look toward the fall campaign with control of Congress at stake.

Beginning in 2011, pharmaceutical industry discounts would cover 50 percent of the costs of drugs that seniors buy once they enter the gap in coverage. That share would rise to 75 percent over a decade. That would bring it into line with the program's basic benefit, in which Medicare recipients generally pay 25 percent of their costs and the program picks up the rest.

To help pay the cost of increased benefits, the legislation would increase Medicare payroll tax 0.9 percentage point, to 2.35 percent, on wages above $200,000 for individuals and $250,000 for married couples filing jointly.

In a change sought by the White House, beginning in 2013, a new 3.8 percent tax would be imposed on interest, dividends, capital gains and other investment income for individuals making more $200,000 and couples making more than $250,000.