DETROIT — Labor unions usually dread bankruptcy, and for good reason. Their pay, benefits and pensions typically suffer significant cuts, as airline and steel workers can attest.

But for the United Automobile Workers union, Chrysler’s Chapter 11 case, which began in New York on Friday, could turn out to be — if the company survives and thrives — the Cadillac of bankruptcies.

The U.A.W., for example, has received upfront protection from the Treasury Department for its pension plan and the fund that will take over responsibility for retiree medical benefits.

Moreover, that fund, called the voluntary employee beneficiary association, or VEBA, will control 55 percent of the equity in the new Chrysler once it emerges from bankruptcy, and hold a seat on the Chrysler board.

Of course, those hard-fought gains, and the big ownership stake, could be worthless if Chrysler does not make it. And the company’s fortunes continued to sag in April, when sales fell 48 percent compared with the same month in 2008. Chrysler will also have to wait roughly two years or more for new cars designed by its partner, the Italian automaker Fiat, to show up in Chrysler dealerships.

But for now, even though Chrysler workers had to agree to lower pay and less generous benefits as part of the deal, the U.A.W. appears to be enjoying relative safety in helping steer the course of the Chrysler bankruptcy.

“I’m very comfortable,” Ron Gettelfinger, the U.A.W.’s president, said Friday on National Public Radio. “It’s not like we’re going into this bankruptcy fighting with Chrysler and Fiat and the U.S. Treasury. We’re going in there in lockstep to put our agreements in place.”

Labor and restructuring lawyers said such a comprehensive deal going into bankruptcy was rare.

“This is extraordinary, truly extraordinary,” said Mary Jo Dowd, a partner in the financial and bankruptcy restructuring practice at Arent Fox in Washington. “I never would have thought a year ago that this would occur. These are truly unusual times.”

Asked if he could recall any other union that fared as well, David L. Gregory, a labor law professor at St. John’s University, replied: “Nobody’s even close.”

But the U.A.W. is also no ordinary union. Even though its membership at the Detroit automakers has shrunk to a quarter of its size in 1990, it still maintains tremendous influence in Washington, partly because of its heavy political contributions.

The government, in assessing what was needed to make Chrysler viable, decided it needed to support workers, as well as suppliers, and guarantee the warranties on Chrysler vehicles.

Because the union agreed to negotiate, it was made a partner, with the government and Fiat, in developing the plan to restructure the company.

In contrast, other companies often use bankruptcy as a way to gain leverage over labor, so that they can lower their costs. Workers at Bethlehem Steel, United Airlines, Delta Air Lines and US Airways lost all or most of their traditional pension benefits when those employers sought bankruptcy protection in this decade, though some of the shortfall was covered by the federal government. Retiree health care coverage was also cut.

None of those cases, filed during the Bush administration, had the kind of federal support offered to the U.A.W.

In the case of Chrysler, the Treasury is giving the VEBA a $4.6 billion note, payable over 13 years at a 9 percent interest rate, helping to fund roughly $10 billion in liabilities. The rest will be paid in Chrysler stock. Chrysler’s pension plans will be preserved, with the help of $600 million from Daimler, Chrysler’s former owner, the Treasury said.

If Chrysler goes under, pensions will be covered in part by the federal pension agency, but workers will receive much less than they are owed. The VEBA would be in dire straits, since it would owe the Treasury and have nothing to pay it back with.

The U.A.W. was ready for the probability of a Chrysler filing as far back as two months ago, people involved in the negotiations said. Its stand was clear: for it to support a bankruptcy case, workers’ health care and pensions had to be protected.

But the administration, advised by Ron Bloom, the veteran restructuring expert, also insisted that the union make sacrifices. On Wednesday, Chrysler workers approved concessions, including work rule changes, that would result in lower pay and less generous benefits than in the 2007 contract.

Significantly, the VEBA can begin adjusting workers’ health care benefits in 2010, two years sooner than the previous contract allowed.

Chrysler workers’ concessions, similar to those granted earlier this year at Ford Motor, form the basis of a prenegotiated labor agreement with the new Chrysler, people involved in the negotiations said.

Chrysler’s pension liability will shift from the defunct company to the new one, these people said, and workers will continue to have a lucrative contract.

Despite the concessions, Chrysler’s most senior workers, like those at Ford, still have healthy wages and benefits; bountiful health care coverage, at least until it is adjusted; and subsidies to help bolster unemployment benefits they receive while plants are closed, as they will be at Chrysler for weeks until the sale is final.

That carryover is unusual, Ms. Dowd said, since the buyers of assets in bankruptcy cases normally try to purchase them free and clear of their existing liabilities.

It also means the union will not have to come to terms with Fiat once it takes over the company, or risk having its contracts abrogated.

None of this sat well with some Chrysler’s debtholders, who questioned the fairness of the 55 percent stake granted to the VEBA. They did not raise objections in bankruptcy court on Friday, however.

Professor Gregory said the U.A.W.’s position still carried risk.

“Chrysler may be worth nothing, and 55 percent of nothing may be worth nothing,” he said. But a comeback by Chrysler after it emerges from bankruptcy could ensure the security of the retiree health care fund, which will begin selling its Chrysler shares as soon as possible, Mr. Gettelfinger said Friday.

His legacy, and that of the union, could also could benefit, Professor Gregory said — if Chrysler and G.M. are able to successfully restructure.

“It’s walking a very tight rope without a safety net, and a very high wire,” he said. “But if this can get some traction, they could be the envy of not just organized labor, but a lot of folks.”