Legislation to enact President Barack Obama's top domestic goal, remaking US health care, was expected to clear a new Senate procedural hurdle Tuesday and stay on track for Christmas passage.

The early morning vote, set for about 7:20 am (1220 GMT), was to come one day after the sweeping bill overcame its toughest challenge and won exactly the 60 votes necessary to set the stage for a final ballot on Christmas Eve.

Obama praised his 58 Democratic allies and their two independent cohorts for sealing "a big victory for the American people" in the dead-of-night vote that he said "knocked down" a Republican effort to doom the bill.

"The Senate has moved us closer to reform that makes a tremendous difference for families, for seniors, for businesses, and for the country as a whole," the president said in remarks at the White House.

The measure also got the support of the influential American Medical Association (AMA), which represents the interests of nearly a quarter-million US doctors.

"America has the best health care in the world -- if you can get it -- but for far too many people, access to care is out of reach," said Doctor Cecil Wilson, the organization's president elect.

Republicans vowed to fight the legislation every step of the way and, unable to bring parliamentary delaying tactics to bear against the 60-vote Democratic majority, seemed to pin their hopes on a collapse when the Senate and House of Representatives try to negotiate a compromise plan to send to Obama.

Democrats hope the Senate and the House, which passed its version November 7, will agree quickly enough to enable the president to sign the most sweeping overhaul of its kind in four decades before his State of the Union speech in late January or early February.

But Democrats who control both chambers are at odds over tough new curbs on federal monies going to pay for abortions and the Senate's decision to strip out a government-backed "public option" to compete with private insurers.

There are other rifts -- and centrist Senate Democrats who rallied behind the bill at the last minute have warned they will help kill the bill if the House-Senate "conference" makes major changes to the legislation they shaped.

"The House of Representatives will have to basically back down on virtually everything they passed for this to become law. It will be interesting to see whether there's any institutional pride over there," said Republican Senate Minority Leader Mitch McConnell.

Asked about the likely difficulty of agreeing on a final bill, Democratic Senate Majority Leader Harry Reid told reporters "we'll worry about the next steps at a later time."

"Right now we're focused on what we're going to do this week," he said. "We're going to finish this bill before Christmas."

On Monday, Obama sought to refute on key Republican argument, saying his critics' frequent charge that the measure will further inflate the ballooning US budget deficit, swelling the country's debt, "does not hold water."

Obama pointed to estimates from the non-partisan Congressional Budget Office (CBO), which found the bill would reduce the deficit by 132 billion dollars over the first 10 years and as much as 1.3 trillion in the next 10.

Republicans have said that the CBO typically takes at face value assumptions in legislation it is asked to assess, and that the Congress will scrap some central but politically painful cost-cutting provisions in the bill.

Republicans have also vowed to make their opposition to the measure a rallying cry in next year's political campaign ahead of mid-term elections in November.

"We have just begun to fight," said Republican Senator John McCain, Obama's defeated rival for the White House in 2008.

A new public opinion poll released by CNN television found that 42 percent of those surveyed supported the Senate's version, up six points from earlier this month, but still well below the 56 percent who oppose it.

The United States is the world's richest nation but the only industrialized democracy that does not provide health care coverage to all of its citizens.

Washington spends more than double what Britain, France and Germany do per person on health care, but lags behind other countries in life expectancy and infant mortality, according to the Organization for Economic Cooperation and Development (OECD).