Thomas K. Mayes, 47, an assistant with the Office of Protective Security at the Department of State who had been an agent of the U.S. Secret Service for 10 years, died Friday at his home in Oakton following a heart attack.

Mr. Mayes, who was born in Oak Park, Ill., was a graduate of the University of Illinois and received a master's degree there in 1962. In the interim between his undergraduate and graduate work, Mr. Mayes served as a Foreign Service officer. He had been assigned to posts in Washington and Guyana.

He came to Washington in 1963, and began his career with the Secret Service. The following year, he was made assistant special agent in charge of the service's presidential office. In 1966, he was appointed to the same post in the vice presidential office.

Mr. Mayes became the assistant for operations and logistics in the Office of Protective Operations in 1972. He retired from the Secret Service the following year.

Mr. Mayes came out of retirement in 1976 and became special assistant for protective security at the Department of State. He held that position at the time of his death.

Survivors include his wife, the former Judith Amphlett, and two sons, John and Warren, all of Oakton; a brother, John A., of Glen Ellyn, Ill., and a sister, Janis Nemeth of El Cajon, Calif.

The family suggests that expressions of sympathy be in the form of contributions to the Heart Association of Northern Virginia.