Dr. David McKenzie Rioch, 85, the founding director of the Division of Neuropsychiatry at the Walter Reed Army Institute of Research and a former president of the Washington Psychiatric Institute, died of a heart ailment Sept. 11 at his home in Chevy Chase.

Dr. Rioch began his career in medicine as a surgeon. He became an anatomist and clinical psychiatrist and an authority on the anatomy of the brain and military and social psychiatry. He was a physician, a teacher, a researcher who published more than 100 papers in professional journals, and an administrator who held posts in public and private institutions.

He was a fellow of the American Psychiatric Association, the American Academy of Arts and Science, the Washington Academy of Science and the Washington Academy of Medicine. He was a past president of the Association for Research in Nervous and Mental Disease and the American Psychopathological Association and an honorary member of the American Neurological Association.

Dr. Rioch was born in India, where his parents were missionaries. He graduated from Butler College in 1920 and took his medical degree at Johns Hopkins University in 1924. He did residencies in Boston and Rochester, N.Y., and further study at the University of Michigan, the Central Institute for Brain Research in Amsterdam, and Oxford University, England.

From 1931 to 1938, he was an assistant professor of anatomy at the Harvard Medical School. For the next four years he was chairman of the department of neuropsychiatry at Washington University in St. Louis.

Dr. Rioch moved to Washington in 1943 as a member of the staff of Chestnut Lodge, a private psychiatric hospital in Rockville where he later was director of research, and as executive director of the Washington School of Psychiatry. He was president of the latter from 1947 to 1956.

In 1951, Dr. Rioch became director of the Division of Neuropsychiatry at the Walter Reed Army Institute of Research, of which he was a founder. The institute is part of the Walter Reed Army Medical Center. Dr. Rioch directed neuropsychiatry there until he retired in 1970.

He later was a senior scientist at the Institute for Behavioral Research, a private, nonprofit organization in Silver Spring, and taught at the medical schools of Johns Hopkins University, the University of Chicago and the Uniformed Services University for the Health Sciences.

Dr. Rioch received the Exceptional Civilian Service Award from the Defense Department, the Army Research and Development Achievement Award, the Walter Reed Medal from the Walter Reed Army Medical Center, and the Van Giesen medal of the New York State Psychiatric Institute.

Survivors include his wife, Dr. Margaret Jeffrey Rioch, whom he married in 1938, of Chevy Chase.