SAN FRANCISCO (AP) _ Charles R. Schwab has resigned from the board of directors of BankAmerica Corp., the company announced.

His departure is the second this week by an official of the ailing banking giant. John Poelker said Monday he was resigning as chief financial officer and treasurer to spend more time with his family.

Meanwhile, the San Francisco Chronicle quoted sources as saying Bank of America is negotiating for an infusion of capital from a Japanese concern and has retained an investment adviser to assist in the transaction.

The newspaper said a BankAmerica spokesman confirmed an adviser had been hired, ''but we do that as a normal course of business. We retain investment advisers to assist us in raising capital. That's how you do banking.''

The newspaper also quoted sources as saying Schwab is considering putting together a group of investors to try to repurchase his discount brokerage from BankAmerica.

Schwab, chairman and chief executive officer of Charles Schwab & Co., had been a board member since his firm was acquired by BankAmerica in 1983. He said Wednesday that he is quitting to devote his full attention to the discount brokerage subsidiary and ensure that it is ''the most successful enterprise in the business.''

However, one analyst said Schwab's past criticism of bank policy could have contributed to his resignation.

''The presumption has to be that there's some other reason for his leaving, since we'd like to believe that he's been devoting his energies to the (Schwab) company all along,'' said Dan Williams of Sutro & Co. Inc. in San Francisco.

Samuel H. Armacost, chairman and chief executive officer of Bank of America, said: ''Chuck has been a valuable contributor to the board's deliberations and we respect his wish to concentrate his business attention exclusively on the growth and success of the company he founded.'' Poelker said his resignation was entirely personal and had nothing to do with the bank's problems.

Bank of America, the nation's second largest bank behind Citicorp, last month reported losses of $640 million for the second quarter, or $4.25 per share.

Schwab, meanwhile, had sold off his BankAmerica shares to invest in other areas. His stake in BankAmerica dwindled from a high of about 700,000 shares to about 61,000 shares in April.