Frederick A. Tilton, 73, a retired security official of the Defense Department, died of pneumonia Monday at the Mary Hitchcock Memorial Hospital in Hanover, N.H.

Mr. Tilton moved to Washington from his native Laconia, N.H., in 1955 to begin his career at Defense. He worked first in the office of legislative and public affairs. In 1960, he joined the office security review.

In 1966, he was named to the industrial security review appeal board. He served as its chairman from 1974 until his retirement at the end of 1978.

Mr. Tilton received the Defense Department's meritorious civillian service medal in 1976.

He and his wife, Agnes, returned to Laconia in 1979.

Mr. Tilton attended Dartmouth College and earned a law degree at Boston University. He then practiced law in Laconia and also served three terms in the New Hampshire state legislature.

During World War ii, he enlisted in the Marine Corps. He later held a commission in the Marine Reserves and was recalled to active duty during the Korean conflict. He came to Washington when his service was ended.

In addition to his wife, survivors include two sons, Frederick A. Jr., of Concord Mass., and Army Lt. Col. Franklin T., of Carlisle, Pa.; one daughter, Mrs. Alan A. Ayre of Agawam, Mass.; a brother, Robert P., of Laconia; a sister, Mrs. Russel Clark of Chester, Vt.; 13 grandchildren, and one great-granddaughter.