Sen. Joseph I. Lieberman (I., Conn.), who caucuses with the majority Democrats, said he was "inclined to support" a procedural motion to bring the bill to the Senate floor but remained opposed to a federal-government plan in any form - even with the "opt out" provision for states that Reid (D., Nev.) said Monday he would include in the bill.

"I really want to get to yes," Lieberman said. But unless the public-option language is dropped, he said he would likely align with Republicans to block final passage.

Other party moderates said they remained undecided on the opt-out public plan.

"I'm skeptical about what Sen. Reid has proposed," said Sen. Mary Landrieu (D., La.). Like Lieberman, she opposes a national, government-run insurance plan that would compete with the private sector. But Landrieu gave Reid slightly more leeway, noting that she would "stay open to a principled compromise."

Sen. Thomas R. Carper (D., Del.), a Finance Committee member who prefers any public option to be run by a nonprofit board rather than the government, said: "This is not the end. This is not the beginning of the end. This is the end of the beginning."

The proposed public option has been the main flash point in both the House and Senate as Democrats struggle to pass legislation that would extend coverage to millions of uninsured, ban insurance-industry practices such as denying coverage for preexisting medical conditions, and slow the growth of health-care spending.

Before that issue can be joined on the Senate floor, Reid's first challenge is to gain 60 votes - the number needed to overcome any filibuster by Republicans - just to bring the bill up.

Democrats control 60 votes in the Senate and Reid is trying to secure commitments from the entire caucus to allow the Senate to begin debate on the legislation.

If the party moderates' concerns are unlikely to prevent the bill from advancing to the floor, they do raise prospects that the opt-out provision eventually will be modified.

One alternative could be the "trigger" approach that Sen. Olympia J. Snowe (R., Maine) has advocated that would allow a government plan where private insurance is not available at competitive rates.

Yesterday, Snowe, who voted in favor of the plan that emerged from the Senate Finance Committee - the only Republican vote in either house for a health-care overhaul - said she would vote against bringing the Reid version to a debate on the floor.

Republican leaders said they would try to scuttle the bill before debate begins.

Sen. Mitch McConnell of Kentucky, the GOP leader, said his party would treat the procedural vote as though it were "a vote on the merits" of the bill, which he charged would "cut Medicare, raise taxes, and increase health-insurance premiums."

Reid said he would take the process one step at a time.

"We're going to see what the final product is. We're not there yet," he told reporters.

Reid's more immediate problem may be Sen. Ben Nelson (D., Neb.), who, unlike Lieberman, has not pledged to vote even to permit debate.

While he has not ruled out backing a public plan, Nelson said he wanted to make sure it did not become a "big-government insurance" company.

Nelson said he was concerned also about a proposal to create a new public insurance program for long-term care, known as the CLASS Act (short for Community Living Services and Support).

Because it would begin taking in premiums immediately but wouldn't start paying benefits until 2016, congressional budget analysts have forecast it would generate $60 billion over the next 10 years - helping finance a health package.

But the American Academy of Actuaries has warned it could require infusions of taxpayer money to cover benefits after 2019. Sen. Kent Conrad (D., N.D.) called it "a Ponzi scheme."