CAMBRIDGE, MASS., MAY 29 -- Derek C. Bok announced today that he will step down as president of Harvard University next year, two decades after taking over an institution in turmoil.

Bok, 60, said the timing of his move was influenced by the unexpected departure of Michael Spence, dean of the faculty, and the planned start of a vast fund-raising effort. He said his successor should appoint the new dean and be in place to finish the capital campaign.

Calling it "an extraordinary privilege" to serve as Harvard's 25th president, Bok said he had "very few disappointments" about his tenure and cited with satisfaction his emphasis on training public servants and introducing ethics throughout the curriculum.

"I came in at a very turbulent time, and things were pretty chaotic," Bok said in an interview. "I have had the benefit of staying on as there has been greater and greater calm and stability and good humor. So I come away without any regrets. The job has been more wonderful than I expected."

Bok has had a major impact on the 354-year-old university. He is credited with building the John F. Kennedy School of Government into a major professional school, introducing a new "core curriculum" for undergraduates and gradually increasing numbers of women and minorities among students, faculty and staff.

With a low-key lawyerly style, the former dean of Harvard Law School steered the school through a period of student unrest that hurried the departure of his predecessor, Nathan Pusey. Bok also presided over growth of Harvard's endowment from $1 billion in 1971 to nearly $5 billion.

During his tenure, however, Bok was criticized for resisting calls to divest Harvard's holdings in companies doing business with South Africa, which it eventually did. Bok also has been faulted for not moving faster to diversify the faculty, notably at the law school where Professor Derrick Bell has taken a leave to protest lack of a tenured black woman.

Bok's successor must be nominated by the seven-member governing corporation and approved by the board of overseers. Many Harvard presidents have been chosen from within.

But the search will be a wide one, according to Henry Rosovsky, former dean of the faculty who has stepped in as acting dean with the departure of Spence for Stanford University. Rosovsky, 63, said he considers himself too old for the president's job.