Dr. Angus C. Tregidga, 70, a physicist and retired assistant to the director of the Johns Hopkins Applied Physics Laboratory here, died Tuesday at a hospital in Seattle, after a heart attack. He had lived in Whidbey Island, Wash., since 1976.

Dr. Tregidga joined the laboratory in 1951 as a specialist in electronics systems design and analysis. He became supervisor of the Bumble Bee missile program homing systems group. He was in charge of the radar homing guidance for the Talos ramjet missile.

He served as an adviser to the Navy's Bureau of Aeronautics on guidance for the Regulus II missile and to the Navy's Bureau of Ships on antisubmarine warfare. He had evaluated the influence satellites would have on naval operations for the Office of Naval Research.

Dr. Tregidga had participated in a study for the Advanced Research Projects Agency of the Defense Department. He was assistant to the director from 1959 until retiring in 1975. He had lived in Silver Spring for 25 years.

He was born in Burnley, England, and moved to British Columbia, Canada, with his family while in his teens. He graduated from the University of British Columbia and took his doctorate in physics from the Colifornia Institute of Technology.

Dr. Tregidga was an electrical engineering instructor at the University of Kansas and then was chief engineer and general manager of the Motorola Inc. plant in Phoenix before joining the Johns Hopkins Laboratory.

He is survived by his wife, the former Ruth Bracebridge, of Whidbey Island; a daughter, Sylvia Burgess of Seattle; a son, Allan, of Palo Alto, Calif., and two grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Whidbey General Hospital, Coupeville, Wash. 98239.