WASHINGTON -- With a close vote looming in the House of Representatives, President Barack Obama's push for healthcare reform was boosted on Thursday by the support of powerful lobbies representing doctors and seniors.

House Democratic leaders struggled to round up enough party moderates to reach the 218 votes needed to pass Obama's top domestic priority ahead of a planned Saturday vote.

Obama will visit the Capitol on Friday to make a personal plea for support. He said endorsements from the American Medical Association representing doctors, and AARP, the lobbying group for older Americans, were a powerful argument.

I urge Congress to listen to the AARP, listen to the AMA, and pass this reform for hundreds of millions of Americans, Obama said in a surprise appearance in the White House briefing room. We are closer to passing this reform than ever before.

Failure in the Democratic-controlled House would be a huge political blow to Obama, and Democratic leaders scrambled to win over some party moderates who have lingering concerns about the bill's cost and its provisions on abortion.

I think it's going to be close, House Democratic leader Steny Hoyer said but added he was confident the bill would get the votes of 218 of the 258 Democrats.

Asked if she had the votes, House Speaker Nancy Pelosi said: We will.

Republicans are united in opposition to the sweeping overhaul, which is designed to rein in costs, expand coverage to millions of uninsured and bar insurance practices such as denying coverage to people with pre-existing conditions.

They have objected to the bill's price tag of just more than $1 trillion and what they say is its excessive government interference in the private healthcare and insurance markets.

A LONG WAY FROM 218

I can't figure out how many votes they've got, Representative Eric Cantor, the No. 2 House Republican, told reporters. But he said Pelosi is a long way from the 218 necessary.

About 1,000 protesters opposed to the healthcare reform effort gathered on the lawn outside the Capitol, waving yellow Don't Tread on Me flags and signs, including one reading Stop the Obama-nation of America.

If the healthcare bill passes the House, action would move to the Senate, which is preparing its own version. Obama wants to sign a bill by year's end, but Senate Democratic leader Harry Reid has indicated that deadline might slip.

AARP said the House bill would help seniors pay for their prescription drug coverage and strengthen Medicare, the government-run health program for the elderly.

We can say with confidence that it meets our priorities for protecting Medicare, providing more affordable health insurance for 50 to 64-year-olds, and reforming the healthcare system, Nancy LeaMond, executive vice president, said.

Along with the doctors' and seniors' lobbying groups, the American Cancer Society also endorsed the bill.

The overhaul would spark the biggest changes in the U.S. healthcare system since the creation of the Medicare health program for the elderly in 1965. Congressional budget analysts said it would extend coverage to 36 million uninsured people living in the United States,

The House bill would require individuals to buy insurance and all but the smallest employers to offer health coverage to workers. It also would provide subsidies to help purchase insurance and would eliminate the industry's exemption from federal antitrust laws.

Many changes in the bill would only take effect in 2013.

House Democratic leaders are trying to address the concerns of about 40 members who want to be sure federal subsidies are not spent to pay for abortions. Democrats who support abortion rights want to ensure the bill does not exceed current restrictions on using federal money to finance abortions.

The Senate's version of a healthcare bill has been bogged down as Reid awaits cost estimates from congressional budget analysts and searches for an approach that could win the 60 votes needed to overcome Republican procedural hurdles.

Republican Senator Jon Kyl said failure or a very close vote in the predominantly Democratic House would give pause to some moderate Senate Democrats from conservative states who have not committed to backing the healthcare measure.

It will be very difficult for folks in those places to support the kind of legislation that Harry Reid is going to put on the floor, Kyl told reporters.

The House and Senate bills both include a government-run public insurance option that Obama and supporters say would create competition in the insurance market. Critics say it would lead to a government takeover of the sector.

If the two chambers pass their bills, the differences would have to be reconciled before a single reform bill goes to Obama for his signature. I think we can do all this before Christmas, Pelosi told reporters.

(Additional reporting by Andy Sullivan; Editing by Alan Elsner)

Healthcare Eric cantor Barack obama Nancy Pelosi