After passing the largest expansion in the history of the 38-year-old Medicare program Tuesday, Senate GOP leaders declined to adjourn the chamber sine die and left open the option of calling Senators back the week of Dec. 8 for what could be a very contentious effort to pass an omnibus spending bill.

With appropriators and the White House unable to reach final agreement on the shape of the omnibus until today, Senate Majority Leader Bill Frist (R-Tenn.) sent Senators home for the Thanksgiving holiday and convened a series of press briefings designed as valedictories to the GOP’s efforts through the first session. Frist said he was waiting to see what the House would do in the coming weeks before making a final decision and would consider calling the chamber back into session.

“I think probably that means not sine die now,” Frist told reporters, adding later, “I’ll keep all options open. That’s why I don’t want to close the place down now.”

At one point Republicans had considered seeking unanimous consent to adjourn with a resolution saying the chamber was closed for business, but would approve the omnibus once the House passed it next month — an idea Democrats flatly rejected because of their opposition to several controversial provisions believed to be in the final version of the bill.

“There’s a possibility now that we will be coming back Dec. 8. I don’t think we could possibly U.C. it,” Minority Leader Tom Daschle (D-S.D.) said.

“The omnibus is dead unless they take stuff out of it,” Minority Whip Harry Reid (D-Nev.) proclaimed before heading to the airport for a flight out of town. Whether the debate comes in December or January, Reid said Democrats specifically object to any alteration of the provision passed in both chambers barring the Federal Communications Commission from instituting new rules for media ownership sought by its chairman, Michael Powell, as well as several other provisions.

House Republican leaders, meanwhile, remained determined to reconvene Dec. 8 for a one-day session to wrap up the year’s business.

GOP leaders said Tuesday that regardless of the Senate’s plans, they will bring the House back in two weeks to consider the omnibus. Once Members pass the spending measure, the House will adjourn until Jan. 20.

“We want to get our work done,” said John Feehery, spokesman for House Speaker Dennis Hastert (R-Ill.). “We’re going to come back in December and get the omni bill done.”

Feehery said Republican leaders will continue to encourage their Senate counterparts to return in December to complete the appropriations process. House leaders filed the omnibus conference report on Tuesday.

Frist now faces a choice: He could let the House pass the omnibus next month and keep the Senate out until its planned start date of the second session of the 108th Congress, Jan. 20, and risk being attacked for not doing the people’s work. Or, Frist can make a decision that will be very unpopular with many of his colleagues and call the Senate back for a heated debate the week of Dec. 8.

Sen. Ted Stevens (R-Alaska), Appropriations chairman, indicated he would be willing to come back to work in December, as did Daschle: “If that’s what it takes.”

The confusion over the schedule, however slightly, muddled what otherwise was arguably the single biggest achievement of Frist’s brief tenure as leader — passing the nearly $400 billion Medicare bill that included a prescription drug benefit for some seniors. In a somewhat surprisingly narrow vote, 54-44, Republicans mustered enough support to pass what may prove to be their most politically important domestic policy priority.

Two of the Democratic presidential contenders, Sens. John Kerry (Mass.) and Joe Lieberman (Conn.), did not vote today on the measure after returning home from the campaign trail over the weekend to help lead a failed filibuster attempt Sunday and Monday.

Twelve Democrats supported the measure, and nine conservative Republicans opposed it.

“The victory is for the American people,” Frist said, declining to claim what was obviously a big political win for the Republicans.

But Democrats said they were ready to pounce on the issue, beginning to work on how best to frame what they consider to be a political albatross around the GOP’s neck, whether in direct mail pieces in the near term or political attack ads next fall. “We’re working on how to frame it,” said Sen. Jon Corzine (N.J.), chairman of the Democratic Senatorial Campaign Committee.