Dr. Leon Yochelson, 64, the chairman of the Psychiatric Institute of Washington and a former chairman of the department of psychiatry at George Washington University medical school, died of cardiac arrest June 22 at George Washington University Hospital.

An authority on the relationship between law and psychiatry, Dr. Yochelson was a former cochairman of the university's Institute of Law, Psychiatry and Criminology. In addition to teaching and writing on the law and psychiatry, he often was called as an expert witness in trials where testimony on forensic psychiatry was needed.

He joined the medical faculty at GWU as an assistant clinical professor in 1949 and held the rank of professor of psychiatry and behavioral sciences at his death. He also had taught at Catholic University, Howard University, the University of Oklahoma and elsewhere.

He was a training and supervisory analyst at the Washington Psychoanalytic Institute for many years. In addition to serving as chairman of the Psychiatric Institute of Washington, he was chairman of the Psychiatric Institute Foundation, its research and education arm. He was chairman of the Psychiatric Institutes of America.

As a private physician, Dr. Yochelson had maintained a practice in psychiatry here since 1948. At his death, he was chairman of Professional Associates, a group practice.

A native of Buffalo, N.Y., he earned bachelor's and medical degrees at the University of Buffalo. After an internship at St. Elizabeths Hospital in Washington, he served in the Army in the Pacific and Australia during World War II.

After the war, he returned here and graduated from the Washington School of Psychiatry and the Washington Psychoanalytic Institute. He was a staff physician at George Washington University Hospital, Sibley Memorial Hospital, the Children's Hospital National Medical Center and the Psychiatric Institute of Washington.

Dr. Yochelson was an examiner of the American Board of Psychiatry and Neurology, a charter member of the American Academy of Psychiatry and Law, a fellow of the American College of Psychiatrists, and a member of numerous other professional organizations.

Survivors include his wife, Ruth Jolley Yochelson of Washington, and three children, David, of California, and Roger and Deborah, both of Washington.