WASHINGTON—Desperate U.S. automakers ran into fresh obstacles from skeptical lawmakers Thursday as they appealed with rising urgency—and a new dose of humility—for a $34 billion bailout. Without help, said one senator, “we’re looking at a death sentence.”

With lawmakers in both parties pressing the automakers to consider a pre-negotiated bankruptcy—something they have consistently shunned—the Big Three were contemplating a government-run restructuring that could yield results similar to bankruptcy, including massive downsizing, in return for the bailout billions. But there was no assurance they could get even that.

And that wasn’t all the unwelcome news. Congressional officials said during the day that one leading proposal—to tap an already-approved fund supposedly set aside for making cars environmentally efficient—wouldn’t give the carmakers nearly as much money as they say they need.

The auto executives pleaded with lawmakers at a contentious Capitol Hill hearing—their second round in as many weeks—for emergency aid before year’s end. But with time running out on the current Congress, skepticism about the bailout appeared to be as strong as ever.

“In all due respect, folks, I don’t think there’s faith that the next ... three months will work out given the past history,” said Sen. Charles E. Schumer, D-N.Y.

“No thinking person thinks that all three companies can survive,” said Republican Sen. Bob Corker of Tennessee.

Chris Dodd, chairman of the Banking Committee, was the senator who spoke of a death sentence—though he also said, “We’re not going to leave town without trying” to help.

The auto executives are to make their case at a House hearing on Friday, and Congress could take up rescue legislation next week in an emergency session.

No one was talking optimistically about their chances, and the skepticism wasn’t limited to Capitol Hill.

President George W. Bush said in an interview with NBC News, “No matter how important the autos are to our economy we don’t want to put good money after bad. In other words, we want to make sure that the plan they develop is one that ensures their long-term viability for the sake of the taxpayer.”

President-elect Barack Obama was keeping his distance, and Rep. Barney Frank, D-Mass., who has been dealing with both the financial bailout and the auto rescue proposal, said, “He’s going to have to be more assertive than he’s been.” Frank is chairman of the House Financial Services Committee, which will conduct Friday’s hearing.

Repentant after a botched first crack at bailout pleas, the executives from General Motors Corp., Ford Motor Co. and Chrysler LLC all agreed during Thursday’s session that a multibillion-dollar bailout deal would include a supervisory government board that could order major overhauls of the companies if deemed necessary for survival.

United Auto Workers union President Ron Gettelfinger, aligned with the industry in pressing for the aid, told senators that any kind of bankruptcy, even a pre-packaged one, was not “a viable option.” Gettelfinger said consumers would not buy autos from bankrupt companies, no matter the terms of the arrangement.