BankAmerica Corp., already hobbled by two years of massive losses, announced yesterday that it was setting aside $1.1 billion for possible future losses on loans to troubled Third World borrowers. As a result, the San Francisco banking company will post a second-quarter loss of $1 billion.

The move effectively delays for at least a year the return to profitability promised by Chief Executive A.W. Clausen when he returned to the bank last fall. Although the bank did not release an estimate of its full-year loss, analysts said the company would probably record a net loss in 1987 of about $800 million.

This year's loss follows deficits in 1985 and 1986 totaling $855 million, which left BankAmerica, once the nation's largest bank, crippled. Over the past two years, the company suspended its common stock dividend, sold nearly 20 percent of its assets, changed its entire top management and fought off an unwelcome takeover attempt by Los Angeles' First Interstate Bancorp.

The bank took the step reluctantly after a special meeting of its board of directors yesterday. Clausen said just 10 days ago that he believed the bank's bad-loan reserve was "adequate" but that the company might be forced to raise it to counter a widespread "perception" that it was too small.

The huge second-quarter loss will bring new pressure on BankAmerica, parent of Bank of America, to strengthen its underlying capital base. The company's common shareholders' equity is now a tenuous 2.3 percent of the bank's total $99 billion in assets, a ratio that BankAmerica will try to improve by disposing of additional assets or selling new securities, perhaps to a group of Japanese banks.

Clausen was in Japan last week to meet with the leaders of Japan's largest banks. Although the bank would not discuss the subject of the meetings, reliable Japanese newspapers said that Clausen was seeking commitments from the Japanese to buy $300 million in new BankAmerica securities.

Frank Newman, chief financial officer, denied the possibility that BankAmerica's move was prompted by a poor reception in Tokyo. "There actually is no connection," Newman said, adding "we would generally be pleased to have Japanese investors {participate} in our future securities offerings."

With this action, BankAmerica is recognizing that a sizable proportion of its $10 billion in loans to developing countries will never be paid back. Clausen said the move will strengthen BankAmerica's hand in negotiating with foreign borrowers and improve the bank's ability to withstand future shocks.

The addition to the loan loss reserve essentially transfers money from one BankAmerica account to another and, while it will result in a large loss for the year, does not affect the safety of depositors' funds.

Major U.S. banks are following the lead set by New York's Citicorp, the nation's largest bank holding company, which added $3 billion loan loss reserves last month. Citicorp said the action would result in a second-quarter loss of $2.5 billion and a loss for the year of $1 billion.

Over the past three weeks, a number of the nation's largest banks, including Chase Manhattan Corp., Norwest Corp. in Minneapolis, Bank of Boston and Rainier Bancorporation in Seattle, followed Citicorp in boosting loan-loss reserves and announcing large quarterly losses. Seafirst Corp., a BankAmerica subsidiary in Seattle, said yesterday that it was adding $60 million to its bad-loan account.

"This addition to our reserve will allow us to address the new uncertainties introduced by the changes in market perception and will strengthen our ability to help develop constructive solutions to the developing-country debt situation," Clausen said.

The banks' actions mark a new chapter in the evolving Third World debt saga. The moves were prompted by Brazil's unilateral suspension of interest payments on $67 billion in foreign loans in February.

Clausen said BankAmerica's loan-loss reserve now amounts to about 25 percent of the total amount owed by public and private borrowers in 45 developing countries.