WASHINGTON - House Democratic leaders struggled yesterday to contain uprisings on the hot-button issues of abortion and illegal immigration that have left them little margin for error as they try to push through a health-care overhaul bill this weekend.

While confident of victory - and boosted yesterday by the endorsements of the American Medical Association, the powerful seniors lobby AARP, and the American Cancer Society - House Speaker Nancy Pelosi and other Democratic leaders were working to contain defections to the roughly 25 Democrats already viewed as "hard no" votes.

There will be 258 Democrats in the House by the time the vote occurs, but to secure the 218 votes needed for passage - and with prospects dim for Republican converts - Pelosi can afford to lose no more than 40 members of her caucus.

President Obama was set to head to the Hill this morning to rally wavering Democrats to get behind the bill.

For party leaders, setting a weekend deadline for passage represented a calculated risk, one that could backfire if the vote, now expected late tomorrow or Sunday, either fails or must be delayed.

But leaders feared that if members were given more time to consider the bill, it was likely new issues would flare up, particularly as lawmakers digest the results from Tuesday's elections.

Most ominous for Democrats were their losses in gubernatorial contests in New Jersey and Virginia, although the party did prevail in House elections in New York and California.

The legislation's prospects got a lift with endorsements from the AARP, the AMA, and the cancer society.

AARP, with its 40 million members, promised to run ads and contact activists to gin up support.

AMA president James Rohack said that while it's "not the perfect bill," it "goes a long way toward expanding access to high-quality affordable health coverage for all."

The 10-year, $1.2 trillion legislation would cover 36 million uninsured and create a government program - the so-called public option - to compete with private insurance.

'Right on the brink'

But Pelosi was still working to chip away resistance from antiabortion Democrats, who worry the bill could lead to government funding of the procedure, and from Hispanic members trying to stave off a provision that would bar illegal workers from buying private insurance policies through new federally established marketplaces, even with their own money.

"We are right on the brink of passing historic legislation," Pelosi told reporters. Asked whether she had the votes to bring the bill to the House floor, she said: "We will."

The legislation's next stop is the Rules Committee, which meets today to establish a framework for debate on the biggest expansion of health coverage since Medicare and Medicaid were created in 1965.

Rules Chairwoman Louise Slaughter (D., N.Y.) said more than 50 amendments had been filed by members of both parties and debate was expected to consume at least five hours of floor time tomorrow. Procedural maneuvering by Republicans could extend that by several hours.

Potential land mines

The final House bill is expected to vary just slightly from the 1,990-page document Democratic leaders unveiled last week.

As written, it allows plans offered through new insurance exchanges, set up for individuals without employer coverage, to cover abortion services.

But the plans would be required to establish payment fire walls to prevent federal subsidies from covering the cost. Democrats opposed to abortion call that an accounting distinction and are seeking ironclad guarantees.

As the hours ticked away, Democrats scrutinized the bill for potential land mines that could hurt them on the campaign trail next year.

The prospect that Republicans will identify a loophole that could be construed as benefiting those who live in the United States illegally is receiving a great deal of attention.

House leaders are considering accepting more restrictive Senate language on illegal immigrants. That upsets Hispanic members.

"Yes, you have someone here illegally, that's a bad thing," said Rep. Charles Gonzalez (D., Texas). "But they are here. And someone's hiring them, by the way, and paying them. And they want to be responsible for their health care. We're going to have a provision that disallows them from purchasing a private plan?"

Of yesterday's endorsements, the most significant was from AARP.

Republicans have blasted the House bill as devastating for seniors, pointing to more than $400 billion in Medicare cuts over the next 10 years.

AARP vice president Nancy LeaMond said the House package would strengthen Medicare, the health program for people over 65, by restraining its skyrocketing costs.