PITTSBURGH (AP) _ Mellon Bank today announced the retirement of Chairman J. David Barnes, who had been under pressure since acknowledging management mistakes that led to the first quarterly loss in the bank's 118-year history.

The board of directors, meeting Sunday, elected its senior member, Nathan W. Pearson, 75, to fill the vacancy until a newly formed search committee can find a new chairman and chief executive.

Mellon on Friday confirmed what Barnes had predicted April 2, a $60 million first-quarter loss and a 50 percent reduction of the common stock dividend. He said it was unclear when the bank's finances could be turned around.

The bank was hurt by troubled loans to developing nations, primarily Brazil, and loans to the energy-dependent Southwest United States.

''Mr. Barnes felt a change in management at this time would help the bank move more quickly and with less constraint in meeting the needs of shareholders, customers and employees,'' Pearson said in a statement.

Barnes, 57, joined Mellon in 1956. Officially, he retired from the bank and resigned as a director of the bank and its parent company, Mellon Bank Corp., the nation's 12th-largest bank-holding company.

Board member Andrew W. Mathieson, 58, will heard the search committee.

Pearson, financial adviser to the Paul Mellon Family Interests, has been a director since 1972.