The director of the National Institute of Mental Health (NIMH) will return after a two-year absence to reassume the head psychiatric post at the Harvard-affiliated McLean Hospital, the hospital announced this week.

Dr. Shervert H. Frazier will complete his leave of absence from the 328-bed Belmont psychiatric hospital after heading the world's largest research center for mental health, which allocated nearly $204 million in 1986.

"I don't get a chance to see any patients," Frazier said of his work at NIMH. "I'm a clinician, and I want to go back and do what I want to do."

During Frazier's leave of absence, the non-profit hospital's search committee did not select a permanent director. Frazier will serve as psychiatrist-in-chief until a permanent director is chosen, said McLean General Director Francis deMarneffe.

Frazier, a professor of psychiatry at Harvard Medical School, will resume teaching, and will serve as chairman of the Harvard Department of Psychiatry at McLean.

Frazier, 65, said he does not plan to return to NIMH. "I don't think I would be offered the opportunity," he said. "I don't plan to shuttle."

"I like Washington, and I don't plan to be disengaged from it. I'm just going to be on the other side of the fence," he said yesterday.

Frazier first came to McLean as psychiatrist-in-chief in 1972. Before that he was deputy director of the New York State Psychiatric Institute and professor of clinical psychiatry at Columbia University College of Physicians and Surgeons.

Dr. Alan Schatzberg, who served as interim psychiatrist-in-chief will continue at McLean as a psychiatrist and co-director of the hospital's Affective Disease Program.