NEW YORK (AP) -- Shares of General Motors Corp. fell below $1 on Friday for the first time in 76 years as the struggling automaker approached a government-imposed restructuring deadline and a likely filing for Chapter 11 bankruptcy protection.

Shares rebounded to 89 cents by late morning.

The symbolic drop comes just days ahead of a government-mandated June 1 deadline to restructure. GM is expected to file for Chapter 11 bankruptcy protection by then, which would leave existing shareholders virtually wiped out.

A senior Obama administration official estimated that GM would be under bankruptcy protection for 60 to 90 days, longer than Chrysler LLC's expected reorganization because GM is bigger and more complex. The official spoke on condition of anonymity because of the sensitivity of the negotiations.

GM's new road map, outlined in a regulatory filing Thursday, would briefly send the automaker into bankruptcy protection, erase most of its debt and eventually have it emerge leaner and stronger.

GM offered a new debt-for-equity exchange to its bondholders on Thursday as it sought to put the pieces in place for a quick bankruptcy process. The offer would give the bondholders a 10 percent stake in a reorganized GM, plus warrants to buy another 15 percent, in exchange for retiring their $27 billion in unsecured debt.

Under the terms of the new offer, the bondholders would agree not to oppose a quick sale of most of GM's assets under Chapter 11 protection. A key group of institutional bondholders backed the new terms on Thursday.

All told, the U.S. government would own 72.5 percent stake in the restructured automaker after it emerges from bankruptcy protection. A United Auto Workers trust that will take over retiree health care expenses will get 17.5 percent, and the old GM, effectively owned by the bondholders, would get the rest. The plan made no mention of the fate of existing shareholders.

On Thursday, a person familiar with GM's plans said it was "probable" that the company would file for Chapter 11 bankruptcy protection Monday. The person did not want to be identified because the plans were still under discussion with the U.S. and Canadian governments.

Chrysler, meanwhile, was in bankruptcy court in New York on Friday where a judge is hearing a motion on whether to sell the bulk of its assets to Italian automaker Fiat Group SpA. Chrysler has been operating under bankruptcy protection since April 31.