AFP - President Barack Obama's top domestic priority, remaking US health care, cleared a major Senate hurdle but strong opposition Sunday to key parts of the proposals augured a tough battle ahead.

After a knife-edge vote on Saturday night, battle lines were already being drawn on Sunday with the leading Republican in the Senate, Mitch McConnell of Kentucky, warning Democrats of a long road ahead.

"Just to look at recent legislative activities on the Senate side, we spent four weeks last Congress on a farm bill, seven weeks creating the Department of Homeland Security a few years ago, eight weeks on an energy bill.

"The Senate doesn't do things quickly," he said.

America's Thanksgiving holidays are set to be marked by bitter debate over the nitty-gritty of the bill, from its costs in terms of tax increases and fees to the merits or not of the so-called "public option" on health care insurance.

Divisive issues like abortion funding could also come to the fore as Democrats and Republicans face off on what would amount to the biggest shake-up of US health care in four decades.

Unsurprisingly, reactions to Saturday's decision to allow the bill to proceed to the floor of the Senate for debate were, like the vote itself, strictly along party lines.

Democratic senator Dick Durbin of Obama's home state of Illinois hailed "an amazing victory" for the president, but Republican senator Kay Bailey Hutchison of Texas called it a "terrible bill" and a "disaster for our country."

Formal debate in the Senate was expected to begin November 30, after next week's Thanksgiving break, and to last at least three weeks as senators battle over possible changes to the legislation.

Republicans hope to kill the bill or delay the battle into next year with the expectation that the 2010 midterm elections may make it harder for moderate Democrats to support it.

Senators voted 60-39 Saturday to formally start debate on legislation aimed at extending coverage to some 31 million Americans who currently lack it.

Obama's Democratic allies mustered the bare minimum 60 votes needed to take up the bill in the Senate, rallying wavering colleagues and independents to defeat 39 of the chamber's 40 Republicans, one of whom was absent.

The Senate bill includes a government-backed insurance program to compete with private firms, the controversial so-called "public option," and restrictions on dropping care for pre-existing ailments.

It is estimated to cost 848 billion dollars through 2019 but cut the sky-high US budget deficit by 130 billion dollars over the same period.

The leading Democrat in the Senate, Harry Reid, faced three possible defectors, any one of whom could have deprived him the 60 votes necessary to prevent Republican parliamentary delaying tactics.

Those senators -- Mary Landrieu of Louisiana, Blanche Lincoln of Arkansas, and Ben Nelson of Nebraska -- have signaled a willingness to join Republicans if their proposed changes to core provisions of the bill are defeated.

Landrieu and Lincoln are strongly opposed to the government-backed "public option," but Nelson indicated on Sunday that he could be open to persuasion on the issue.

"We could negotiate a public option of some sort that I might look at, but I don't want a big government, Washington-run operation," he told ABC's "This Week" program.

Nelson has said he wants tougher restrictions on federal money subsidizing abortions, mirroring language the House of Representatives added to its version of the bill when it approved it in a 220-215 squeaker November 7.

A successful final vote -- expected a month away at the earliest -- would force the Senate and the House of Representatives to reconcile their rival versions of the bill and vote again on whether to send it to Obama.

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, about 36 million of whom are uninsured.

Several US presidents since Theodore Roosevelt in the early 1900s have sought to overcome the traditional US suspicion of a wider government role in health care.

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).