WASHINGTON - A year in the making, sweeping health-care legislation backed by President Obama hung in the balance yesterday as conservative Democratic Sen. Ben Nelson withheld his vote in pursuit of stricter abortion limits, and liberals grew restive on the left.

Any lingering hopes the bill's supporters had of a Republican casting a critical 60th vote vanished when Sen. Olympia Snowe of Maine said after a meeting with Obama that the Democrats' timetable for a pre-Christmas vote was "totally unrealistic."

"I hope we're getting closer" to agreement, Nelson said. Earlier in the day, the Nebraska senator said in a written statement summarizing results of days of private negotiations: "Without modifications, the language concerning abortion is not sufficient." He opposes abortion and wants tighter restrictions written into the bill.

With his support, the White House and Senate Democrats would command 60 votes for the health-care measure, enough to overcome a Republican filibuster and pass the bill within days.

Without it, the prospects are far more uncertain, given unyielding Republican opposition on the conservative right as well as growing expressions of unhappiness on the left that sent the White House scrambling.

"The absolute refusal of Republicans in the Senate to support health-care reform and the hijacking of the bill by defenders of the insurance industry have brought us a Senate bill that is inadequate," Richard Trumka, head of the AFL-CIO, said in a statement.

His criticism of GOP lawmakers aside, Trumka's blast seemed aimed at Nelson, Joe Lieberman (I., Conn.), and possibly other members of the Senate Democratic caucus who have successfully stripped the legislation of any form of government-run insurance option.

Andrew Stern, head of the Service Employees International Union, said he, too, was deeply disappointed in the bill. But he stopped short of urging its defeat.

Not so Howard Dean, the former national party chairman, who has said he would oppose the bill because it does not include a strong enough role for the government in a remade health-care system. Dean unleashed his criticism this week after Lieberman won deletion of a proposed expansion of Medicare from the bill.

Overall, the legislation aims to extend coverage to millions who lack it, ban insurance company practices such as denying coverage because of pre-existing conditions, and slow the rise in medical spending.

The bill would require most Americans to buy insurance, and it includes hundreds of billions of dollars in subsidies to help lower- and middle-class families afford it.

Former President Bill Clinton, who failed to win a health-care overhaul in the 1990s, issued a statement saying, "Allowing this effort to fall short now would be a colossal blunder, both politically for our party and, far more important, for the physical, fiscal, and economic health of our country."

Liberal supporters of the bill in the Senate renewed their support as well. Sen. Tom Harkin (D., Iowa) said debates "leading to the passage of Social Security in 1935 and Medicare in 1965 were no less turbulent and partisan."

The Catholic Health Association, which opposes abortion, issued an optimistic statement on the compromise talks to date on the issue.

"Especially now that a public health-insurance option is no longer on the table, we are increasingly confident that Senator [Bob] Casey's language can achieve the objective of no federal funding for abortion," said Carol Keehan, its president and chief executive officer.

Casey (D., Pa.), who has strong antiabortion credentials, has been leading efforts to find a compromise that could win Nelson's support.

Nelson, in a radio interview, cast doubt on whether there was still time to complete work on the legislation before Christmas, the informal deadline set by the Democratic leadership.

As drafted, the Senate bill bans the use of federal funds to finance abortions under insurance to be sold in a newly created exchange, except in cases of rape, incest, or danger to the life of the mother.

The plans could provide abortion coverage, however, that consumers would buy with their own money held apart from any federal subsidies they receive. Abortion opponents say that approach is an accounting gimmick.