WASHINGTON? Senators readied for a crucial pre-dawn Monday vote to pave the way for US health care reform, President Barack Obama's top domestic priority, after a key holdout senator said he would back the sweeping legislation.

Democratic Senator Ben Nelson's resistance had kept fellow Democrats from corralling the 60 votes needed to ensure Senate passage over resistance from Republicans eager to hand Obama a crippling political defeat.

"Change is never easy, but change is what is needed in America today. I will vote for health care reform," said the Nebraska lawmaker, who announced Saturday he had secured the tough new restrictions he sought on public money from paying for abortions.

"With today's developments," Obama told reporters at the White House, "it now appears the American people will have the vote they deserve on genuine reform offering security to those who have health insurance and affordable options for those who do not."

While acknowledging "there is still much work left to be done," the president hailed what he called "a major step forward for the American people."

"After a nearly century-long struggle we are on the cusp of making health care reform a reality," he said.

But groups from opposites sides of the abortion debate assaulted the compromise. The pro-choice National Organization of Women called it a "cruelly over-compromised legislation," while the conservative Family Research Council blasted the "phony abortion 'compromise.'"

The House of Representatives approved similar curbs on abortion when it passed its own version of the legislation, but abortion-rights Democrats have vowed to strip them when the two chambers craft a final bill for Obama to sign into law.

Nelson warned? "less as a threat, and more of a promise"? that he would oppose the final House-Senate compromise if it included "material changes" that stripped out his demands, likely dooming the legislation.

His backing allowed Democrats to breathe a sign of relief ahead of a make-or-break 1:00 am (0600 GMT) Monday vote to end debate on Democratic Senate Majority Leader Harry Reid's newly unveiled compromise health bill.

A tentative Democratic timeline also calls for key procedural votes around 7:00 am (1200 GMT) Tuesday and 1:00 pm (1800 GMT) Wednesday, with final passage at 7:00 pm Thursday (0000 GMT Friday)? Christmas Eve.

If the Senate approves the bill, it will still need to reconcile stark differences with a House plan to pass a final measure before Obama's State of the Union address to the US Congress in January or early February.

Reid's measure strips out a government-backed "public option" plan to compete with private insurers, but would extend coverage to 31 million of the 36 million Americans who currently lack it, Democrats say.

It would forbid insurers from denying coverage because of pre-existing medical conditions and provide subsidies to low-income Americans.

Obama's Republican foes have sharply criticized Reid for only making the bill public Saturday and then pushing ahead with an accelerated schedule in order to meet a self-imposed Christmas deadline.

And Republicans made good on pledges to delay the bill at all costs? forcing the Senate clerk to read the measure aloud, a process that took up most of the day.

"We will do everything in our power to stop it," vowed Republican Senator John Cornyn.

As a severe snowstorm pounded the US capital, Democrats took steps to ensure that they could call upon all 58 of their senators and the two independents who often side with them to prevail in the coming votes.

And they trumpeted a finding from the non-partisan Congressional Budget Office that the bill would cost 871 billion dollars over the next 10 years and cut the soaring US budget deficit by about 132 billion dollars? bringing it in under Obama's top pricetag of 900 billion dollars.

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).