General Motors Corp. said yesterday it plans to restate earnings for 2001, and possibly for the past five years, over an issue related to one of multiple investigations into the automaker's accounting by the Securities and Exchange Commission.

In an SEC filing released after the close of financial markets, GM said it estimates that its 2001 profit was overstated by $300 million to $400 million, or 25 percent to 35 percent. The automaker said it has not determined the final restatement amount for that year or subsequent years. A spokesman for GM would not comment on the filing or other SEC investigations.

Earlier yesterday, GM's credit rating was lowered another two notches by Fitch Ratings, which indicated that the automaker may incur costs related to the bankruptcy of parts maker Delphi Corp.

The credit-rating news sent GM's shares tumbling to their lowest level since 1992, closing at $24.63 on the New York Stock Exchange.

GM said the restatement is related to an SEC review of so-called supplier credits, which are payments that auto suppliers make to GM to compensate for faulty parts. The government has been interested in how GM accounted for those payments. In general, if a part does not work properly, GM does not absorb the total cost of fixing the part but instead seeks a payment from the supplier.

In its filing, GM said the company erroneously recognized some supplier credits as income in the year in which they were received rather than in the future periods to which they were attributable.

Additionally, the SEC has been investigating how GM accounts for its pension obligations. The agency is interested in whether GM properly accounted for its separation of Delphi, which had been a division of GM before it was split off as a separate company in 1999.

Under terms of the separation agreement, GM pledged to take on certain retiree pension costs if Delphi were to go bankrupt. Delphi filed for Chapter 11 protection last month. Within days of the bankruptcy filing, GM disclosed that its pension liability for Delphi workers could be as high as $11 billion. In October, GM reported that the SEC has issued subpoenas for information relating to pensions and transactions with Delphi.

This year, Delphi restated earnings for the past five years, ending a 10-month internal accounting probe that led to the ouster of five executives. The company reduced 2001 retained earnings by $265 million and 2002 profit by $24 million and narrowed its 2003 loss by $46 million. Delphi also said its 2004 loss widened to $4.8 billion from the $36 million it had reported.

In a separate SEC filing yesterday, GM revised its financial results for the second quarter of this year to record a much wider loss of $1.07 billion, nearly four times the $286 million loss it had previously reported. The results were adjusted to reflect a decline in the value of GM's 20 percent stake in the Japanese company Fuji Heavy Industries Ltd., which builds Subarus in the United States and Japan. GM said last month that it plans to sell that stake.

General Motors's financial condition has been steadily deteriorating this year. GM's core North American division is deep in the red. GM has been hit particularly hard by the collapse of the once-booming market for large sport-utility vehicles, a major source of profit for the company. Company executives are busy trying to pull off a turnaround plan, which includes pay and benefit concessions from plant workers. GM is also looking to sell part of its profitable GMAC loan-financing business.