WASHINGTON — In a blow to the White House, the Senate’s top Democrat signaled Tuesday that Congress may fail to meet a year-end deadline for passing health care legislation, leaving the measure’s fate to the uncertainties of the 2010 election season.

Majority Leader Harry Reid, D-Nev., spoke as Democratic officials said it could be December before Senate debate begins in earnest on the issue atop President Barack Obama’s domestic agenda, months after senior lawmakers and the White House had hoped. The drive to pass legislation has been plagued for months by divisions within the party’s rank and file.

House leaders, on a somewhat faster track, pointed toward a vote this weekend on a bill to extend coverage to tens of millions who lack it, ban insurance industry practices such as denying coverage because of pre-existing medical conditions and generally slow the rate of growth of medical spending nationwide. The 10-year, $1.2 trillion legislation is estimated to expand coverage to about 96 percent of eligible Americans.

The measure includes an option for consumers to purchase a government insurance plan, an attempt to put pressure on private firms.

While Speaker Nancy Pelosi, D-Calif., and House leaders weighed final changes to their version of the bill, Reid for the first time publicly raised the possibility that lawmakers would not be able to meet their — and Obama’s — self-imposed deadline of completing work on health care by year’s end.

“We’re not going to be bound by any timelines. We need to do the best job we can for the American people,” he said after the weekly closed-door meeting of rank-and-file Democrats.

A few hours later, Reid’s office revised his remarks. “Our goals remain unchanged. We want to get health insurance reform done this year, and we have unprecedented momentum to achieve that. There is no reason why we can’t have a transparent and thorough debate in the Senate and still send a bill to the president by Christmas,” said spokesman Jim Manley.

At the White House, spokesman Reid Cherlin sought to put the best face on the developments. “We’re moving on the same timeline. The House plans to vote on the health reform bill within days, and as Senator Reid said today, he shares the White House’s commitment to passing meaningful reform by Christmas and will be moving swiftly once the Senate hears back from CBO,” he said.

The Congressional Budget Office is preparing cost estimates of a draft bill Reid completed last week.

Any delay past Obama’s oft-repeated year-end timetable would put the issue off until the 2010 election year and inevitably raise doubts about Democrats’ ability to deliver on behalf of the Obama administration.

Despite the late-afternoon statement, numerous other officials said it could be early December before the Senate begins work in earnest on long-delayed health care legislation, making it a virtual impossibility for lawmakers to send a compromise to Obama’s desk by the end of the year.

It has long been obvious that Reid would need 60 votes to overcome a threatened Republican filibuster. As late as last week, when he announced his intention to include a government insurance option in the bill, he avoided saying he had enough support to prevail.

Democrats in both houses have been plagued all year by internal divisions on the issue, a problem more difficult for Reid to manage because he must have unanimous support of his rank and file as he tries to overcome solid Republican opposition.

Pelosi, by contrast, leads a caucus of 256 Democrats, and can afford more than two dozen defections and still be assured of passing legislation when the roll is called in the House. She projected no concern about a possible delay in final action until next year.

“Our members know they have an historic responsibility and an historic opportunity to do something great, and we would hope that it would be sooner but I don’t think anybody has a clock ticking,” she said.

Officials said Democrats were still deciding whether to jettison a provision creating a new long-term care insurance program to help seniors and disabled people stay out of nursing homes. Because the government would collect premiums for several years before any benefits were issued, the measure would raise an estimated $70 billion over 10 years — money that would have to be replaced before the health care bill could be completed.

The officials spoke on condition of anonymity, saying they were not authorized to discuss details.

Across the Capitol, House Republicans readied an alternative bill that bore little similarity to the Democratic blueprint.

A copy obtained by The Associated Press called for loosening numerous restrictions on the insurance industry as a way of expanding coverage. As an example, it would permit firms to sell policies across state lines without having to submit to regulations in every state.

It contained none of the tax increases or Medicare cuts that Democrats rely on.

Unlike in the Democratic bills, the Republican draft would permit insurers to continue denying coverage on the basis of pre-existing medical conditions. They also would be permitted to charge higher premiums for individuals who fail to enroll in a “standards-based wellness program.”

The measure would place caps on medical malpractice lawsuits, limiting the amount of damages that could be awarded as well as the size of attorney fees. It also called for the permanent ban on federal funding for most abortions. Current restrictions must be renewed annually.

“We believe it’s going to resonate with millions of Americans who don’t want this massive government takeover of health care to become law,” Rep. Mike Pence, R-Ind., said in a reference to the Democrats’ legislation.