WASHINGTON - Democrats were poised Sunday to pass historical health-care reform legislation that will undoubtedly become the defining moment of Barack Obama's presidency and likely determine whether it stretches into a second term.

It's the most ambitious U.S. social program since Lyndon B. Johnson's Great Society reforms of the tumultuous 1960s and Franklin D. Roosevelt's New Deal that emerged from the trauma of the Great Depression in the 1930s.

Obama appeared set to eke out the narrowest of victories in the House of Representatives in a rare Sunday session that could result in his cherished US $940 billion health-care overhaul finally becoming law.

John Larson, the chairman of the House Democratic caucus, said Sunday his party had the 216 votes needed to pass the bill as Democrats behind the scenes were busy assuring their skittish colleagues that the legislation will not lead to federal funding of abortion.

"We have the votes now -- as we speak," Larson said Sunday on ABC's "This Week."

Later Sunday, another Democrat holdout on abortion emerged to say a deal had been reached on abortion funding. Tom Stupak, a congressman from Michigan, said he and several others would now vote in favour of the bill, adding that meant the legislation would easily pass in the House.

"We're well past 216," he told a news conference.

The health-care bill would provide millions of Americans with something Canadians have long taken for granted -- health insurance, and the peace of mind that a life-threatening illness will not result in financial ruin.

The U.S. is the only country in the developed world that does not provide some form of government health insurance to its citizens, and an estimated 50 million Americans lack any coverage at all. And yet the debate about health-care reform has been a searingly divisive one.

Several presidents have attempted to enact health-care reform legislation, but legendary suspicion by Americans of big government and fears that subsidized health care amounts to socialism have long served to put the brakes to those initiatives.

Obama made a weekend appeal to Democrats still on the fence about the legislation to give the green light to "the single most important step that we have taken on health care since Medicare" was created in 1965. On Sunday, he was at the White House getting updates on the progress in the House of Representatives.

A president who was previously unsuccessful in overhauling the nation's troubled health-care system -- Bill Clinton -- made calls over the weekend to urge waffling Democrats to throw their support behind it.

Republican leaders, meantime, were vowing to repeal the legislation if it became law in the event they recapture control of Congress in the mid-term elections in November.

They have assailed Obama's health-care overhaul for a year, with one describing it as the president's "Waterloo," and warning the Democrats will pay the ultimate price in eight months for pushing through the legislation.

As the threats, pleas and wheeling and dealing continued all weekend at the Capitol building, thousands of irate protesters gathered outside shouting at Democrats to "kill the bill!" Nancy Pelosi, speaker of the House of Representatives, was heckled Sunday as she lead the Democratic delegation into the Capitol.

On Saturday, protesters hurled insults at black and gay lawmakers in scenes that occasionally taint the right-wing demonstrations against Obama's agenda. Black legislators say they were called the N-word as they entered the Capitol building, while Democrat congressman Barney Frank said he was called a "faggot."

House leaders from both parties, speaking on NBC's "Meet the Press" on Sunday, condemned the racial taunts.

"It's certainly not a reflection of the movement or the Republican Party when you have idiots out there saying stupid things," said Michael Steele, the black chairman of the Republican National Committee.

If Democratic leaders were to succeed Sunday in passing all three House health-care reform votes scheduled, Obama could sign the Senate version of the bill into law in the days to come.

Another bill of tweaks to the primary health-care package would go to the Senate, and likely be passed in the next week under a complex congressional procedure known as reconciliation that requires only 50 votes in the 100-member Senate.

Such parliamentary manoeuvres became necessary when a Republican recently won the late Ted Kennedy's Senate seat. That gave Republicans the ability to stop the legislation dead in its tracks with a filibuster.

But in a possible sign that Democrats are confident they could win the votes in the House on Sunday, they dropped plans for another controversial parliamentary tactic called "deem and pass." Instead, they're going for a simple yes-or-no vote on the bill.