Navy Cmdr. James T. Dalton, 43, a Medical Service Corps officer who had served as executive assistant to the Assistant Secretary of Defense for Health Affairs since 1977, died Tuesday at the National Hospital for Orthopaedics and Rehabilitation in Arlington after a heart attack. He lived in Alexandria.

Cmrd. Dalton, who was born in Arcadia, Calif., enlisted in the Navy in 1958 as a hospital corpsman. He served as a pharmacy technician for six years before being commissioned into the Medical Service Corps in 1964. After attending the Naval School of Health Care Administration in Bethesda, which gave him the Surgeon General of the Navy Award for Scholastic Achievement in 1970, he earned a bachelor's degree in health care administration from George Washington University and a master's degree in financial management from the Naval Postgraduate School in Monterey, Calif.

A former academic director of the Hospital Corps School in San Diego, Cmdr. Dalton also served as an aide to the commanding officer of the Naval Regional Medical Center in Lakland, Calif., and as a medical administrator aboard the aircraft carrier USS Hornet.

His other awards include the Navy's meritorious service and achievement medals.

Cmdr. Dalton's marriage to Dale Halene Dalton of Rockville ended in divorce.

Survivors include two sons, Jeffrey and Lance, and a daughter, Lori Ann, all of Rockville; his mother, Mary Jane Gerlinger of Redding, Calif., and a sister, Debbie Moritz of Salem, Ore.

The family suggests that expressions of sympathy be in the form of contributions to the Navy Relief Society in Arlington.