A $15 billion automaker bailout appears headed toward defeat in the Senate, as Republicans in that chamber said it needs significant revisions before they will support it.

Though the House is moving forward with a vote Wednesday on a measure that was crafted by Democrats and the White House, Sen. Judd Gregg (R-N.H.) said support among GOP Senators was “marginal at best.”

“Obviously, there are significant reservations [for Republicans], and it’s hoped those reservations could be addressed before there’s a vote” in the Senate, said Gregg, ranking member of the Budget Committee.

Gregg and others said the main sticking point for those who want to help the troubled car makers is that the “car czar” needs to have more authority to force restructuring changes of the auto companies.

“Nobody wants to let the auto companies go down. Now how do we prevent that in a way that makes sense? … I think the present bill needs a little more work,” Sen. Bob Bennett (R-Utah) said. “The creation of the car czar is absolutely essential to the resolution of this.”

But a visibly angry Sen. George Voinovich (R-Ohio) said Republicans had a chance over the past few weeks to air their concerns, but declined invitations from Democrats and the Bush White House to participate in talks.

“The White House gave us a real shot to participate and the leadership claimed we didn’t want to participate … because they felt that whatever came out of the negotiations they probably couldn’t support,” said Voinovich, who is one of the few Republicans to support the measure as is.

Voinovich said some GOP votes might be swayed with changes to the car czar language, but complained, “Some of them, frankly, don’t want to do anything.”

Other GOP Senators were moving to draft an alternative that Republicans could support. Sen. Bob Corker (R-Tenn.) said he was currently working on such a measure.

Senate Minority Leader Mitch McConnell (R-Ky.) said Republicans had a “spirited” debate during their luncheon about the auto industry rescue plan, but he said he personally has not decided whether to vote for it. He said he is still reviewing the text.

Senators and GOP aides said few Members spoke in favor of the legislation during the lunch, and that many more expressed their concerns or outright opposition. A handful of GOP Senators, led by Sens. John Ensign (Nev.) and Richard Shelby (Ala.), have threatened to filibuster the measure, which would at the very least force delays in its consideration in the Senate.

Senate Democrats said they were unsure of their next move, but Senate Majority Leader Harry Reid (D-Nev.) indicated early Wednesday that he would file a motion to force a test vote on Friday. Because of the filibuster threat, 60 votes are needed.

With Senate Democrats currently holding only a 51-49 majority, Democrats have said they expect they would need between 12-15 Republicans to vote with them. Not all Democrats are expected to support the measure, some are out of town on official business, and President-elect Barack Obama’s seat is still vacant.

One Senate GOP aide said supporters of the bailout were trying to win over Republican Senators who either are retiring at the end of this Congress or who lost their re-election bids this year.

Meantime, the House is planning to vote on an auto package today, and adjourn, according to senior Democratic sources. Those sources say Democratic leaders will not sine die the chamber, however, leaving open the opportunity to call Members back into session to reconsider the matter.