Moderate Democratic Senators who may have the most to lose from the rancorous health care reform debate are holding their ground and preparing to support the final version of the legislation.

With all Republicans remaining firmly opposed, just one Democratic defection could dissolve Majority Leader Harry Reid’s (D-Nev.) 60-vote coalition and sink a negotiated House-Senate health care bill. But nearly four weeks of falling poll numbers since the Senate approved its reform bill apparently hasn’t scared off centrist Democrats — including those who have taken the brunt of the criticism at home, their offices confirmed late last week.

“This bill is important to people in Louisiana and across the nation,— moderate Sen. Mary Landrieu (D-La.) said last week in a YouTube video that she filmed for her constituents.

Republicans cannot block a united Democratic Conference from passing the health care bill. But the GOP, which aggressively cultivated public opinion against the reform effort last year, will re-engage its messaging assault on the Senate majority this week as it eyes the 2010 midterm elections and holds out hope of forcing one Democrat to reconsider.

Republicans plan to renew charges that Democrats are engineering a government takeover that will worsen the federal deficit, increase taxes, endanger Medicare and diminish the quality of care. The GOP also intends to capitalize on events by focusing attention on the closed-door nature of the health care negotiations and a deal struck with organized labor to temporarily exclude union members from a 40 percent excise tax on expensive insurance plans.

With the RealClearPolitics average of polls gauging support for health care legislation now at 41 percent — 51 percent disapprove — Republicans view their opposition as a win-win. Buoying the GOP are President Barack Obama’s job approval ratings, which early this month hit their lowest point of his presidency. The RealClearPolitics average shows 48.4 percent approving of how Obama is doing his job; 45 percent disapprove.

“We’ll maintain a very high level of intensity communicating as much as possible about the horrible proposal and secretive process being used to write the bill,— a Republican Senate aide said Friday. “Even though Democrats are trying to hide the sweetheart deals they’re cutting behind closed doors, we’re going to work hard to make Americans aware of the details that are leaking out.—

At press time Friday, Obama and Congressional Democratic leaders remained locked in negotiations to reconcile the Senate’s $871 billion health care package passed on Christmas Eve with the $1.2 trillion House version approved before Thanksgiving. Clearly, the outcome of those talks and the final form of the negotiated bill could affect its support among moderate Democratic Senators.

A wild Massachusetts special election to replace the late Sen. Edward Kennedy (D) set for today could also affect the political calculus of health care reform. A victory by Republican state Sen. Scott Brown over state Attorney General Martha Coakley (D) would give Republicans the one additional vote they need to sustain a filibuster of the final health care bill.

But as Democratic centrists were gearing up last week to return to Capitol Hill after the holiday recess, they maintained their support for health care reform, as long as the bill doesn’t deviate substantially from the Senate bill. A couple of liberal Senators who had also threatened to oppose health care reform if it lacked a public insurance option are also holding steady, including Sens. Russ Feingold (D-Wis.) and Bernie Sanders (I-Vt.).

The offices of Landrieu and Virginia Democratic Sens. Mark Warner and Jim Webb said their positions have not changed since December, when they voted for the Senate bill. Sen. Joe Lieberman (ID-Conn.), who caucuses with the Democrats, also supports the bill, his office confirmed. Sen. Ben Nelson (D-Neb.) said in an interview last week that he remains on board.

Webb conceded Thursday during a local radio interview that he has several problems with the Senate’s health care bill, telling the program’s hosts: “I voted with the Republicans I think eight times — more than any other Democratic Senator except perhaps Ben Nelson.— Webb was referring to amendment votes.

Webb criticized his leadership for a negotiating process that he claims lacked transparency and was critical of the provisions in the House and Senate bills that call for cutting nearly $500 billion from Medicare over 10 years and eliminating the Medicare Advantage program popular with many seniors.

But despite his concerns, Webb expects to vote “yes— when the reconciled package hits the Senate floor — so long as it does not deviate too substantially from the legislation approved by the Senate. In practical terms, that means Webb and other Democratic moderates are ready to support a final bill that does not include a public insurance option, does not raise income taxes and stays close to the $900 billion cost ceiling laid out by Obama last September.

Nelson also is demanding that the Senate bill’s language allowing states to decide whether abortion procedures are eligible for insurance coverage not be weakened.

“The reality, when you’re up here is, when something’s in front of you, and if it’s 50.1 percent to the yes side, you pull the lever and vote ‘yes,’— Webb said.

Democratic Sens. Evan Bayh (Ind.) and Blanche Lincoln (Ark.) have not given any indication that they will withhold their support, although their offices declined repeated requests for comment.