Democrats united Saturday night to narrowly push historic health-care legislation past a key U.S. Senate hurdle over the opposition of Republicans eager to inflict a punishing defeat on President Barack Obama.

The 60-39 vote cleared the way for a bruising, full-scale debate beginning after the American Thanksgiving weekend. The legislation, which is designed to extend coverage to roughly 31 million who lack it, would crack down on insurance company practices that deny or dilute benefits and curtail the growth of spending on medical care nationally.

The spectator galleries were full for the unusual Saturday night showdown, and applause broke out briefly when the vote was announced. The 60 votes in favour were the minimum required for the bill to move forward.

In a measure of the significance of the moment, senators sat quietly in their seats, standing only when they were called upon to vote.

In the final minutes of a daylong session, Majority Leader Harry Reid accused Republicans of trying to stifle a historic debate the nation needed.

"Imagine if, instead of debating whether to abolish slavery, instead of debating whether giving women and minorities the right to vote, those who disagreed had muted discussion and killed any vote," he said.

The Republican leader, Senator Mitch McConnell, said the vote was anything but procedural — casting it as a referendum on the bill itself, which he said would raise taxes, cut Medicare and create a "massive and unsustainable debt."

For all the drama, the result of the showdown had been sealed a few hours earlier, when two final Democratic holdout senators, Mary Landrieu of Louisiana and Blanche Lincoln of Arkansas, announced they would join in clearing the way for a full debate.

But both stressed they were not committing in advance to vote for the bill that ultimately emerges from next month's debate.

Of particular contentiousness to moderates is a provision for the government to sell insurance in competition with private companies, subject to state approval.

At the White House, press secretary Robert Gibbs issued a statement saying the president was gratified by the vote. Gibbs said it "brings us one step closer to ending insurance company abuses, reining in spiraling health care costs, providing stability and security to those with health insurance, and extending quality health coverage to those who lack it."

The legislation would require most Americans to carry insurance and provide subsidies to those who couldn't afford it. Large companies could incur costs if they did not provide coverage to their workforce.

The insurance industry would come under significant new regulation under the bill, which would first ease and then ban the practice of denying coverage on the basis of pre-existing medical conditions.

Congressional budget analysts put the legislation's cost at $979 billion US over a decade and said it would reduce deficits over the same period while extending coverage to 94 per cent of the eligible population.