Although they have yet to achieve the "gang" status accorded to previous centrist coalitions, a dozen or so moderate Democrats are emerging as pivotal to the fate of the overhaul measure - starting with the procedural vote that Senate Majority Leader Harry Reid (D., Nev.) must win to launch the historic debate.

Moderates have raised numerous concerns about the bill, including the public insurance option that liberals were able to persuade Reid to add last week.

Although Reid included an "opt-out" provision for states that do not want to participate, many moderate Democrats prefer a "trigger" proposal by their lone GOP ally, Sen. Olympia J. Snowe of Maine. Her approach would allow government-backed coverage only in states where private insurers fail to offer broadly affordable plans.

The list of complaints stretches on: Some senators, including Mary Landrieu (D., La.), want to do more to protect small businesses. Sen. Evan Bayh (D., Ind.) has sought to protect the medical-device makers in his home state from hefty fees. Sen. Ben Nelson (D., Neb.) dislikes provisions that would lift antitrust protections for insurers and create a new government insurance program for long-term care.

Resolving these and other disputes could take weeks, making it increasingly unlikely that President Obama will meet his goal of signing a health-care bill by Christmas. Instead, Democrats are pointing to the State of the Union address as a more realistic target.

Reid said yesterday: "We're not going to be bound by any timelines. We're going to do this legislation as expeditiously as we can, but we're going to do it as fairly as we can."

Later, Reid spokesman Jim Manley sought to clarify that the Christmas deadline remained attainable. "Our goals remain unchanged," Manley said. "We want to get health-insurance reform done this year, and we have unprecedented momentum to achieve that."

House leaders, on a somewhat faster track, pointed toward a vote this weekend on a bill that would extend coverage to tens of millions who lack it, ban industry practices such as denying coverage because of preexisting medical conditions, and generally slow the growth rate of medical spending nationwide.

In the Senate, Reid is working to lock down 60 votes against a Republican filibuster aimed at preventing the bill from reaching the floor.

Senate aides said he had received commitments from all but three Democrats: Nelson, Landrieu, and Sen. Blanche Lincoln of Arkansas, who met with Obama yesterday to discuss the bill.

Landrieu said she was working with Snowe to build support for her "trigger" alternative. The opt-out provision, which was offered by liberals as a compromise, has come under increasing scrutiny because of the likelihood that conservative Southern and Western states with large uninsured populations would indeed decline to participate.

The trigger would have the opposite effect, automatically creating a public option in states where private competition failed to make insurance affordable. Obama has praised the idea as a potential compromise.

Moderates have already beaten back a mandate on employers to provide insurance coverage, though liberals are expected to offer amendments on the floor that would impose such a requirement.

Reid's toughest convert could be Nelson, a conservative former insurance executive who has raised numerous concerns about the Senate bill and is not yet ready to agree to let the debate begin.

"I'd rather see the final product up front," Nelson said, "rather than have to go through the process to establish what the final product is."

Although Snowe is expected to vote with Republicans on the initial filibuster, to register her opposition to the "opt-out" clause, she said she would join forces with Democratic centrists to shape a bill that can pass.