WASHINGTON -- A bid to grant Detroit's Big Three automakers $25 billion in loans this week was on the brink of collapse after the automakers' chief executives spent two days testifying before Congress and failed to win many allies.

Lawmakers worked feverishly late Wednesday to hammer out a deal acceptable to all sides, but it seemed a long shot at best.

"We have to face reality, and reality is we've tried a number of different approaches," Senate Majority Leader Harry Reid, D-Nev., said late Wednesday, without giving up all hope. "We'll see what we can work out in the next 12 hours."

The key hurdles remain the source of the $25 billion and whether a deal can be struck before Congress adjourns for the year -- probably later this week. The prospect appears increasingly unlikely.

Democrats want to carve out $25 billion from the $700 billion Wall Street bailout, while Republicans and the White House want to use a $25 billion Energy Department loan program funded in September, dropping restrictions that the money be used to retool factories to build more fuel-efficient vehicles.

Under the Republican proposal, written by Sens. George Voinovich, R-Ohio, and Christopher Bond, R-Mo., in consultation with the White House, the Commerce Department would oversee the loan program. Automakers would be required to "detail any cost control measures required to achieve their financial viability," according to a summary of the bill obtained by The Detroit News.

The government would get equity stakes in the companies -- a share of future profits -- and there would be limits on executive compensation and bonuses. Money repaid by the automakers would be returned to the retooling program.

Democrats led by Sen. Carl Levin, D-Detroit, are in negotiations with the Republicans to hammer out a compromise. "We're down to wording changes," Bond said. He proposed that the Senate take up the measure today. Reid objected because no one had seen the bill yet, but did not rule out a vote if a compromise can be reached.

House Speaker Nancy Pelosi, D-Calif., however, has adamantly rejected the idea of using the retooling money to provide immediate aid to automakers.

The last-minute maneuvering to try to reach a deal came as the Big Three chiefs endured a second consecutive day of grilling on Capitol Hill. The executives appeared before the House Financial Services Committee, many of their responses echoing what they'd told the Senate Banking Committee on Tuesday.

General Motors Corp. CEO Rick Wagoner said that without immediate help, some or all three of the companies would fail. The consequences for GM would be "devastating," he said. "Unfortunately, in the midst of plans and significant progress, we have run out of capital."

Wagoner said that under a worst-case scenario, GM could burn $4 billion or $5 billion every month. "We don't like being here," he said. But with government funding, "we think we have a good shot to make it through next year."

Chrysler LLC CEO Robert Nardelli again warned the automaker could run out of money before the end of the year. "We are doing everything humanly possible to survive," he said.

Ford Motor Co. CEO Alan Mulally disclosed that the automaker had considered filing for bankruptcy.

"We believe it's not a viable option, so we have no plans for bankruptcy," he said, nothing that Ford would not need funds immediately unless the economy worsened.

Wagoner, too, rejected the possibility of bankruptcy, saying GM would have to "liquidate the company because you wouldn't have any revenue." But financial experts said GM and Chrysler had few other options to stem the outflow of cash. They said the two automakers could delay payments, fire salaried employees with little severance or demand immediate wage givebacks from the United Auto Workers union.

Brian Johnson, an auto analyst at Barclays Capital, said it was unlikely a compromise on aid could be struck before Congress adjourns.

"Assuming defeat, GM would have to 'run on fumes' until the next Congress and administration, unless Congress were to reconvene in December to address emergency compromise legislation," Johnson said in a note.

Automakers might then be forced to return to the Treasury Department and Federal Reserve seeking emergency assistance or access to the discount window for funds.

As the outlook for immediate relief dimmed, Detroit Mayor Kenneth Cockrel Jr. lobbied Capitol Hill on Wednesday, and Michigan Gov. Jennifer Granholm cut short a trip to the Middle East to travel to Washington, where she will press for quick aid today. Dealers also blanketed Capitol Hill.

But the mood in Washington remained skeptical.

"The Big Three stand as emblems of the American Dream," said Rep. Spencer Bachus, R-Ala. "Even though all Americans want this industry to succeed, I cannot support a plan to spend taxpayer money to bail them out. A bailout will just push the problem further into the future."

Supporters of quick aid pointed to the fact that the Chinese government was considering granting aid to its struggling auto industry and that the Canadian government late Wednesday said it would offer additional help to automakers.

The White House has urged Congress to allow a vote on the Republican alternative to provide immediate aid.

The White House said it wasn't responsible if the automakers collapsed. "If Congress leaves for a two-month vacation without having addressed this important issue ... then the Congress will bear responsibility for anything that happens in the next couple of months," White House press secretary Dana Perino said.

Wall Street slammed auto shares Wednesday on increasing worries that Congress won't approve a deal this week.

Ford Motor Co. shares fell 25 percent to $1.26, down 42 cents a share to its lowest point in 26 years, and its market capitalization fell to $3 billion. GM shares fell 30 cents, or nearly 10 percent, to $2.79, after touching their lowest point since 1942.

While the debate about aid continues, there are few signs of improvement in the U.S. auto market.

Wagoner said that GM's auto sales in November were slightly better than in October, when demand for GM models dropped 45 percent, but that overall it saw November sales at an annualized rate of 11 million vehicles -- "still very weak by any standard," he said.