Senate Majority Leader Harry Reid (D-Nev.) appears to be urging fellow Democrats to support a national public insurance option that states could opt out of as part of a broader health care reform bill, but several crucial swing votes are not yet on board.

Still, it appeared Thursday that Democratic leaders were strongly encouraging wavering Democrats to at least vote to overcome a GOP-led filibuster, even if they ultimately oppose the final health care bill.

“Would I vote to move forward to consider [a proposal] that I couldn’t support? That’s the other question that’s being asked,— said Sen. Ben Nelson (D-Neb.) of the calculations he and his fellow centrists were making.

Nelson, who along with Sen. Olympia Snowe (R-Maine) has been holding meetings with a small group of moderates, said he has serious reservations about creating a national public insurance option, regardless of the potential for states to opt out.

“The question is how difficult will it be for states to opt out, that’s always the question, and will some states opt out?— Nelson said. “I’m not sure I understand why you want to have a national public option in advance of the states saying there’s a need for one.—

But Snowe — whom both Reid and the White House have been courting, particularly since she is the only Republican to vote for any Democratic health care reform plan — made clear that the opt-out plan is not something she could support. Snowe was the lone Republican to support the Finance Committee’s version of a health care overhaul.

“It’ a public option so I would be opposed,— Snowe told reporters Thursday. “That’s my position and has been my position.— Snowe only supports creating a public insurance option as a fallback if private insurers cannot reduce costs and increase coverage.

However, other Senate centrists said they were not as concerned about creating a public option.

“I’m open to a public option as I’ve told the leader. … It just depends [how] it’s structured on whether I can support it,— said Sen. Mark Pryor (D-Ark.).

But both Snowe and Nelson said their group of five to six centrists is concerned about taking a procedural vote that would officially bring the bill to the floor. Neither Snowe nor Nelson would name the meeting attendees, saying the makeup has changed from day to day, but earlier this week the invitee list included Sens. Mary Landrieu (D-La.), Blanche Lincoln (D-Ark.), Joe Lieberman (ID-Conn.) and Susan Collins (R-Maine.). The group met Tuesday afternoon and Thursday morning.

Nelson said there is “a lot of concern about voting for a motion to proceed without knowing well in advance what’s going to be within the merged bill.— Reid has been working with the White House, Finance Chairman Max Baucus (D-Mont.) and Sen. Chris Dodd (D-Conn.) — the No. 2 Democrat on the Health, Education, Labor and Pensions panel — to merge the two committees’ bills.

Snowe and Nelson noted that centrists want to make sure the underlying bill is acceptable to them before allowing it to come to the floor. They argued that once the measure is officially being debated, it will be difficult to secure the 60 votes necessary to strip key provisions — such as a public insurance option. Sixty votes are needed to overcome a filibuster of any amendment or bill.

“It would take 60 votes to remove anything. That’s the difficulty,— said Snowe. “So I think that’s the important [thing], the whole issue of the 60 votes on the motion to proceed, because it will be very difficult to garner 60 votes to remove anything.—

Snowe added, “The bottom line for the centrists is we want to make sure that this process is approached, you know, in a methodical deliberate fashion, so that it’s not rushed in any way so that it could jeopardize the quality of the legislation that is ultimately submitted to— the Congressional Budget Office.

Having a cost estimate from the CBO has been a requirement of Snowe, Nelson and other moderates before they would vote to proceed to the bill, but Reid has given them assurances that he will get that score before bringing the measure to the floor.

The difficulties of merging the bills — and satisfying centrists and liberals — has forced Reid to adjust his goal for presenting a final bill to the Caucus. While he had hoped to be finished with negotiations this week, senior Senate Democratic aides acknowledged Thursday that a plan would not be presented to fellow Democrats until next week at the earliest.

Plus, difficulty in getting the votes to pass a separate adjustment to Medicare doctors’ payments this week proved a costly distraction for Senate leaders and the White House. Additionally, Thursday’s 6 p.m. negotiating session involving Reid, Baucus, Dodd and White House officials has been replaced by a Senate Democratic leadership meeting at the White House with President Barack Obama.

David M. Drucker contributed to this report.