WASHINGTON -- President Barack Obama trumpeted two major endorsements for his health overhaul push Thursday as House Democratic leaders pushed toward a vote Saturday on the far-reaching legislation remaking the U.S. health care system.

"I am extraordinarily pleased and grateful to learn that the AARP and the American Medical Association are both supporting the health insurance reform bill that will soon come up to vote in the House of Representatives," Obama said in an unannounced visit to the White House briefing room.

AARP is "no small endorsement," Obama said of the 40-million strong seniors' lobby.

"We are closer to passing this reform than ever before," Obama said. "Now that the doctors and medical professionals of America are standing with us, now that the organizations charged with looking out for the interests of seniors are standing with us, we are even closer."

Obama spoke as House Democratic leaders sought to resolve final disputes before bringing their 10-year, $1.2 trillion health bill to the floor on Saturday. Majority Leader Steny Hoyer, D-Md., said leaders expect to have the 218 votes needed to pass the sweeping bill, which would extend coverage to tens of millions of uninsured people and ban insurance companies from turning people away.

Hoyer acknowledged the vote could be tight, though, and timing of action in the Senate remains uncertain.

"I wouldn't refer to it as a squeaker, but I think it's going to be close," Hoyer said in an interview with wire service reporters. "This is a huge undertaking."

The Maryland Democrat said language on abortion and illegal immigrants was still being worked out, but predicted those issues could be solved by Saturday.

"We certainly have well over 218 people who say they want to vote for the bill," Hoyer said.

"The trick is making sure they have a comfort level with the provisions they are particularly focused on to allow them to do so," he said.

Obama planned a rare trip to the House on Friday to try to win over wavering lawmakers.

House Speaker Nancy Pelosi denied that Obama's visit was needed to get Democrats over the top on the vote count. "We are thrilled that he is coming tomorrow, and we can have our conversation before we go into the process of bringing this legislation to the floor," the California Democrat told reporters at her weekly news conference.

Pelosi will have two more Democrats to count on in the wake of Tuesday's elections. Former California Lt. Gov. John Garamendi was sworn in Thursday to a Northern California congressional seat after telling fellow lawmakers he had campaigned for health care in his race. Democrat Bill Owens is being sworn in Friday to represent a New York district long held by the GOP.

Strong opposition persists on the Hill, however, and thousands of conservatives rallied at the Capitol against the Democrats' health care overhaul plan Thursday, chanting "Kill the bill" as they awaited speeches by Republican leaders. One protester carried a sign reading, "Waterboard Congress."

AARP Senior Policy Adviser John Rother said the group favors the House bill because it closes the coverage gap in Medicare prescription benefits, puts strict limits on what health insurers can charge older workers too young for Medicare and creates a voluntary, long-term care insurance program.

"The bill does improve quality, and it improves access," said Rother. "When people hear this message from us, it will have impact." AARP will reach out to its state and local chapters ahead of the House vote, particularly in districts with a large numbers of older people and a lawmaker who's undecided.

The AMA, however, qualified its support of the bill. The organization's president, Dr. James Rohack, said the bill is not perfect, but it meets enough of the organization's goals to deserve its support. But he also said it's also critical for Congress to fix a Medicare payment formula that if left unchanged would lead to a 20 percent cut in fees to doctors next year.

The American Cancer Society Cancer Action Network also announced its support for the legislation Thursday.

With no GOP backing, Democrats will need overwhelming support from within their own caucus. An intraparty disagreement over how to prevent federal funds from being used to pay for abortion has not yet been entirely resolved, though Hoyer said that language being circulated by one anti-abortion Democrat, Rep. Brad Ellsworth of Indiana, seemed likely to be the basis for an agreement.

Ellsworth's language aims to strengthen stipulations already in the bill against federal money being used to pay for abortions. It would still allow people to pay for abortion coverage with their own money.

That distinction doesn't satisfy anti-abortion groups, which dismiss it as an accounting gimmick. They say federal subsidies for insurance coverage would not be clearly segregated from private funds used to pay for abortions.

The U.S. Conference of Catholic Bishops circulated a memo to congressional staff Wednesday saying that it couldn't support Ellsworth's language as written, but Kathy Saile, the group's director of domestic social development, said Thursday the organization was working with Ellsworth and other anti-abortion Democrats to try to come to agreement.

House leaders are also still grappling with illegal immigration, specifically whether illegal immigrants -- who would be barred from getting federal subsidies -- should be able to purchase insurance coverage within new government "exchanges," using their own money.

The White House does not want this allowed, but some members of the Congressional Hispanic Caucus and other Democrats view that position as too extreme. Hispanic Caucus officials were scheduled to meet with Obama at the White House on Thursday.

The House bill would cover 96 percent of Americans, providing government subsidies beginning in 2013 to extend coverage to millions who now lack it. Self-employed people and small businesses could buy coverage through the new exchanges, either from a private insurer or a new government plan that would compete. All the plans sold through the exchange would have to follow basic consumer protection rules.

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Associated Press writers David Espo, Laurie Kellman and Alan Fram contributed to this report.