Senate Democratic leaders battled on multiple fronts Monday to try to rescue their faltering health care reform plan, as a rebellion by Sen. Joe Lieberman (ID-Conn.) over a proposed Medicare expansion threatened to create a domino effect among centrists and forced leaders to explore new ways to get a bill passed by Christmas.

Lieberman hardly represents the only obstacle for leaders, but his decision on Sunday to threaten a filibuster of the bill over a Medicare provision that was originally intended as a compromise with liberals forced Senate Majority Leader Harry Reid (D-Nev.) to reassess his way forward. Reid called a special caucus of all 60 Members of the Democratic Conference on Monday night to discuss whether liberals and some moderate supporters of the Medicare expansion could accede to Lieberman’s demands. And as of press time, it appeared that they would.

Senate Health, Education, Labor and Pensions Chairman Tom Harkin (D-Iowa), entering the meeting, indicated the Medicare provision would likely be tossed out of the compromise. And afterward, moderate Sen. Evan Bayh (D-Ind.) gave this assessment: “A fair summary is, there are a lot of good things here, the process of reform will be ongoing. This isn’t the last time this issue will be addressed, and if there are further improvements that can be made, well then that will be taken up next year or the year after, but that to allow nothing to get done would be the worst outcome of all.—

The White House has let Reid know that it prefers for him to cut a deal with Lieberman in order to get the bill passed by Dec. 25, multiple Democratic sources said. However, several Democrats said they do not know whether Lieberman can be trusted to follow through on any agreements. Democratic sources insist that Lieberman privately told Reid just a week and a half ago that the Medicare expansion would not draw his opposition.

Lieberman’s aides, however, said Lieberman never voiced support for the Medicare buy-in and even expressed his problems with the provision to Reid on Friday.

“The two outstanding issues are: Will Senate progressives be forced to surrender the Medicare buy-in to get Lieberman and, if so, will Lieberman honor that deal,— said one senior Senate Democratic aide. “It would be good if the next personal commitment [Lieberman] made to vote for the bill was made to the president, because it would be a lot harder for him to break that one.—

[IMGCAP(1)]Even his fellow Senators expressed confusion over Lieberman’s most recent filibuster threat. Lieberman first vowed to filibuster any health care plan that contained a public insurance option.

“Sen. Lieberman, it’s my understanding, proposed a similar measure a very few years ago, so I’m not sure why he’s having a hard time with it today,— said Sen. Mary Landrieu (D-La.), a member of the group of 10 Senators who helped craft the compromise Medicare buy-in proposal.

The group Landrieu participated in tentatively agreed to jettison the bill’s public health insurance option in favor of creating a nonprofit health insurance exchange and an expansion of Medicare, among other things. Reid convened the group because of Lieberman and others’ public option threats. Lieberman was initially invited to join the group, but he didn’t participate. Instead, he sent a few staffers to the talks.

Aides said Reid went into damage-control mode Monday to stop other moderates, such as Sen. Ben Nelson (D-Neb.), from following Lieberman’s lead by drawing lines in the sand.

The fear, the senior Senate Democratic aide said, is that Lieberman may act “as a magnet that draws out other people when those people were pretty close to being in the fold at the end of last week.—

With other Democratic centrists expressing concerns about expanding Medicare as well, Democratic aides said Reid had already expected to make revisions to a compromise proposal that had been crafted by the five liberals and five moderates. Unlike other centrists, however, Lieberman appears to have ignored entreaties to withhold judgment until the Congressional Budget Office finishes its official cost estimate of the plan.

Senate leaders found Lieberman’s stance on Medicare surprising given that he campaigned for president in 2004 and for vice president in 2000 on a platform of expanding the federal health program by allowing seniors ages 55 to 64 to buy in to it — just as the proposed Senate compromise would do.

As recently as Sept. 9, Lieberman outlined his support for the Medicare buy-in proposal.

In explaining his opposition to the public insurance option sought by liberals, Lieberman said in an online chat hosted by the Connecticut Post: “My proposals were to basically expand the existing, successful public health insurance programs, Medicare and Medicaid. … When it came to Medicare I was very focused on a group … post 55 [years old], people who have retired early or unfortunately been laid off early, who lose their health insurance and they’re too young to qualify for Medicare and what I was proposing was that they have an option to buy into Medicare early, and again on the premise that that would be less expensive.—

Lieberman spokeswoman Erika Masonhall said Lieberman made those statements before the Senate Finance Committee passed its bill in October and included numerous provisions making it easier for seniors under 65 to afford insurance.

“Any inclusion of a Medicare buy-in for that same age group would be duplicative of what is already in the bill, would put the government on the hook for billions of additional dollars, and would potentially threaten the solvency of Medicare, which is already in a perilous state. The Senator also has concerns that this provision would result in cost-shifting that would drive up premiums for others, including those with employer-based coverage,— Masonhall said.

Meanwhile, Senate Democratic leaders also took friendly fire from the White House, which disputed accounts that Chief of Staff Rahm Emanuel had told Reid to strike an agreement with Lieberman.

White House spokesman Dan Pfeiffer said in a statement: “The report is inaccurate. The White House is not pushing Senator Reid in any direction. We are working hand in hand with the Senate Leadership to work through the various issues and pass health reform as soon as possible.—

But the senior Senate Democratic aide said the White House made its preferences clear, given pursuing the vote of moderate Sen. Olympia Snowe (R-Maine) or trying to use restrictive budget reconciliation rules would likely require extending the debate into next year. Reconciliation is a complicated process that could allow Democrats to pass some pieces of health care reform with 51 votes.

“The reason our options are so narrow is because it’s accepted as a premise that a deal has to be done by Christmas, and that’s a White House imposed-deadline,— the aide said. “Both of those [other] approaches will put you well into the New Year, and that increases Lieberman’s leverage.—

David M. Drucker contributed to this report.