Dr. Melvin T. Johnson, 76, retired medical director of the Civil Service Commission, died Sunday in Concord, N.H., after a long illness.

Named deputy medical director of CSC in 1960, he became director several years later. He retired last year and moved to Concord.

During Dr. Johnson's tenure, the federal government, under a program initiated by President Kennedy, began hiring mentally retarded persons.

In 1968, Dr. Johnson received the National Physicians Award, sponsored by the President's Committee on Employment of the Handicapped and the American Medical Association.

Born in Kanawha, Iowa, he received a medical degree from the University of Iowa. He was in private practice in Columbia, Utah, where he also was an industrial physician with the U.S. Steel Corp. He later practiced in Lake Mills, Iowa, and held state and county health service positions in Iowa and Michigan.

Dr. Johnson joined the federal government in 1947 as medical officer in the St. Paul, Minn., regional office of the Civil Service Commission.

A year later, he came to Washington as chief of the division of employee health at the Agriculture Department, a position he held until 1960. He is survived by his wife, Helen Woods Johonson, of the home in Concord; a son, the Rev. Martin T. Johnson, also of Concord; two sisters, Bernice Wilkins, of Forest City, Iowa, and Evelyn Phillips, of Grand Junction, Colo., and three grandchildren.