SAN FRANCISCO — California electric utility Pacific Gas and Electric Co., which has $9 billion of bank debt outstanding, said Friday that it has filed for bankruptcy.

The news drove down the stocks of regional and money-center banks known to have exposure to the utility.

The company, a unit of PG&E Corp., said in its filing that three of its largest unsecured creditors are Bank of New York Co., which has $2.21 billion of exposure; the former Bankers Trust Co. (now the property of Deutsche Bank), with $1.3 billion; and Bank of America Corp., with $938 million, according to Reuters.

The shares of Bank of America, which identified a “modest” exposure to California utilities in the first quarter, fell 5% early Friday afternoon and ended the day 4.36% lower, at $49.59.

Bank One Corp., which analysts estimate has some exposure, dropped 2.6% during the same period and ended down 3.7%, at $33.61.

J.P. Morgan Chase & Co., which is also believed to be one of Pacific Gas’ larger lenders, dropped 4.8% at midday and was down 4.96% for the day, at $40.39.

The smaller, San Francisco-based Unionbancal Corp., which in its January conference call with analysts said that it had exposure to unnamed California electricity companies, fell 10.4% in the early afternoon. By day’s end the shares had dropped 9.37%, to $26.50.

The American Banker index of the top 50 banks lost 3.11% Friday.

The possibility of a Chapter 11 filing by the utility had been floated for months, and analysts said they expected most banks with exposure to the utility to have allocated reserves already.

Furthermore, many banking companies would have already placed credits to the company in a nonaccrual category, said Campbell Chaney, an analyst at Sutro & Co. in San Francisco. This means that further interest payments on the loans would reduce nonaccrual balances, he said.

The banks that “could get caught are those that have continued to take payments into interest income, even while knowing the company was in financial distress so that when the company files for bankruptcy the bank has to reverse all that accrued interest,” Mr. Chaney said.

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