Angelo Bartlett Giamatti, the Renaissance scholar who once quipped that he would rather be president of baseball's American League, said yesterday that he plans to leave as Yale University president in 1986, at the end of his eighth year.

In his statement, Giamatti said that he will leave "after considerable reflection" and "appreciative of the high privilege of having served as Yale's 19th president, and with profound affection and respect for the whole Yale community."

J. Richardson Dilworth, senior fellow of the Yale Corporation, the school's governing body, praised Giamatti's "enormous contributions to the present well-being of the university." Former secretary of state Cyrus R. Vance was named to chair an eight-member committee to select Giamatti's replacement.

"I never had in my own mind any fixed term," Giamatti said in a telephone interview. "You don't leave when you're starting to get tired. You leave when you're feeling good, so the institution doesn't have to carry you."

Giamatti's announcement follows the pattern set by many university presidents of leaving their jobs sooner and at younger ages, often after being battered by the time-consuming task of running such multimillion-dollar corporations.

Giamatti was 39 when he became Yale's youngest president in December 1977, after a nine-month search. He was expected to stay for more than a decade.

Giamatti said that he had decided to make his retirement announcement in 1984, effective for this year, but delayed his decision because the school was embroiled in protracted labor negotiations.

Restoring Yale's financial health probably will rank among his most remembered accomplishments, school officials and others said.

Yale's $4 million operating deficit in fiscal 1978 was cut to $2.5 million by the end of Giamatti's first year. By fiscal 1981 he recorded the first budget surplus in 15 years, and the budget has been balanced since.

As for his intentions now, Giamatti said only: "If you're the president of Yale, with all due respect, I don't think you have to look for a job."