Clarence F. Castle, 73, a retired official of the Defense Department who was an expert on fire protection and other aspects of physical security and maintenance, died of cancer Sunday at his home in Alexandria.

Mr. Castle was born in Longmeadow, Mass., and grew up there and elsewhere in the Springfield area. He graduated from the University of Vermont in 1928 with a degree in civil engineering.

He then worked for the Factory Mutual Fire Insurance Company in Boston, Chicago and St. Louis.

In World War II, he began his government career. During the war, he was an officer in the Army Corps of Engineers and rose to the rank of lieutenant colonel. Immediately after the war, he took part in the strategic bombing survey of the fire protection branch in the office of the chief of engineers in the Department of the Army.

In 1950, he transfered to the Defense Department. He worked in the office of the assistant secretary of defense for properties and installations. He was a frequent speaker on fire protection.

Mr. Castle was a founder and member of the Fairlington Methodist Church in Alexandria and a member of the Fairlington Kiwanis Club. He was a member of the Alumni Council of the University of Vermont and in 1975 received its Distinguished Service Award. In earlier years, when he lived in Arlington, he was a member of the advisory committee for the Arlington County building code.

Survivors include his wife, Barbara Gray Castle, of Alexandria; one son, Gray, of New Canaan, Conn.; one daughter, Doborah Joy Fountain, of Alexandria; two brothers Charles D., of Tulsa, Okla.; and Warren G., of Springfield, Mass.; one sister, Edith Bostwick, of Feeding Hills, Mass., and six grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Minister's Descretionary Fund, Fairlington Methodist Church, Alexandria.