Bondholders who hold more than $27 billion in G.M. debt have until May 27 to decide whether they will swap their bonds for shares of a restructured G.M. The company has said it needs 90 percent of the bonds to be exchanged in order to meet Treasury Department guidelines to receive billions of dollars in additional government loans. Analysts say that is unlikely to happen.

If not enough bondholders agree to the terms, G.M. is expected to file for bankruptcy protection by June 1.

"We don't have any plan to make modifications at this point," the chief executive, Fritz Henderson, said during a conference call. He added that the terms of the offer were dictated by Treasury officials, who told G.M. it could not give bondholders more than a 10 percent stake in the restructured company.

G.M. plans to give 89 percent of the company to the Treasury and to a new retiree health care fund for the United Automobile Workers union, 10 percent to bondholders and 1 percent to existing shareholders.

Mr. Henderson reiterated his previous assessment that bankruptcy was "probable" but he played down speculation that such an outcome was inevitable. He also said G.M. hoped to contain a bankruptcy to its U.S. operations but that a global bankruptcy was possible.

There remains "the possibility and an opportunity for it to be done outside of a bankruptcy," he said.

Mr. Henderson declined to comment on the status of talks with the U.A.W. or to respond to the union's complaints that G.M. was shifting vehicle assembly work to factories outside the United States. He said it was too early to specify the 13 plants that G.M. planned to close by the end of next year. The plant closures are among a number of cost-cutting steps that G.M. is planning by the end of next year. It also is eliminating 21,000 factory jobs and shedding about 2,600 dealerships across the United States.

G.M. is in talks to sell three of its eight brands - Saturn, Saab and Hummer - by the end of this year. A fourth brand, Pontiac, is scheduled to close in 2010.

Mr. Henderson said G.M. was in talks with two of three bidders for Hummer and that a sale could occur this month.

Regardless of everything else in its restructuring plan, G.M.'s ability to avoid bankruptcy appears to hinge on whether bondholders agree to the debt exchange offer. Kip Penniman, a credit analyst with KDP Investment Advisors, said the offer would fail unless the terms were changed in bondholders' favor.

"G.M. did not make the bondholders an offer that was realistic," Mr. Penniman said. "There's no incentive for them to take stock that is essentially worthless while the U.A.W., for a much smaller claim, gets a much more significant stake in the company."

Shares of G.M. were down 9.3 percent in afternoon trading.