Collas Grant Harris Sr., 74, a retired official of the Central Intelligence Agency and a retired colonel in the Air Force Reserve, died Thursday at Fairfax Hospital following a heart attack.

Since leaving federal service in 1968, Col. Harris, who had lived in Great Falls since 1937, had served as chairman of the Board of Equalization of Rural Property Assessment for Fairfax County. He also had been a member of the land use committee of the Council of Governments and had engaged in other activities to preserve open land and the environment in the Washington suburbs.

Col. Harris was born in Staunton, Va., and grew up there. He moved to the Washington area in the late 1920s. His education included attendance at Washington and Lee, Georgetown and American universities.

He began his government career in the early 1930s with agencies that came into being after the onset of the Depression. In 1934, he went to work at the National Archives. Early in World War II, he took part in the removal of various documents from the Library of Congress to vaults at Fort Knox, Ky.

In 1942, he went on active duty in the old Army Air Corps. His war service included assignments as a combat intelligence officer in the South Pacific. After the war, he returned to the National Archives, where he helped organize special display cases that would help preserve such documents as the Declaration of Independence. He also helped plan of bomb-proof storage area where these documents are kept at night.

In 1952, Col. Harris joined the CIA, where he became a senior intelligence officer. During his years there, he was an assistant Air Force attache to Austrailia and New Zealand from 1956 to 1959. He retired from the CIA and the Air Force Reserve in 1968.

Col. Harris's survivors include his wife, Ann McSwain Harris of Great Falls; two son, Collas G. Jr., of Great Falls, and James Louis of Sterling, Va.; one brother, Claude B., of Alexandria; one sister, Pauline H. Wilson of Harrisonburg, Va., and one grandson.

The family suggests that expressions of sympathy be in the form of contributions to the Great Falls Episcopal Church, 9220 Georgetown Pike, Great Falls, Va. 22066.