Dr. Francis L. Clark Jr., 49, assistant dean of students at Georgetown University Medical School and an expert in the psychology of adolescents and young adults, died of a coronary thrombosis Saturday while visiting the farm of a friend in Keedsyville, Md.

Dr. Clark, an assistant professor of psychiatry at Georgetown, had a national reputation in the field of adolescent psychology. He was the founder of the mental program in the Student Health Services at Georgetown. He also helped develop the Georgetown Summer Workshop in mental health disciplines for clergy. This was one of the first programs of its kind in the United States.

Through his work the Student Health Services, Dr. Clark developed courses of study for Georgetown medical students, psychiatric residents and child pyschiatry fellows.

He was born in Foxboro. Mass and graduated from St. Michael's College in Vermont. He was a 1954 graduate of Georgetown Medical School and served his residency there. He was a captain in the Air Force for two years and then became a faculty-member at Georgetown in 1960.

Dr. Clark was a diplomate of the American Board of Psychiatry, a fellow of the American psychiatric Association, and a fellow of the American College Health Association. He also was a member of the Washington Psychiatric Society snd the Medical Society of the District of Columbia.

Survivors include a brother, Richard, of Foxboro, Mass.

The family suggests that expressions of sympathy be in the form fo contributions to the Georgetown University School of Medicine, Reservoir Road, Washington, D.C.