Col. William C. Farnum (U.S. Army retired), an early army aviator who commanded major air bases in the Pacific during World War II, died Thursday of pneumonia at Walter Reed Hospital. He was 87.

Col. Farnum was a member of one of the U.S. Army's first flying classes in the early 1920s, and flew extensively in fixed-wing aircraft and dirigibles. Shortly after outbreak of World War II, he was named commander of Hickman Field in Hawaii. Later he was garrison commander of the airfield on Tinan Island in the South Pacific, which was used by the plane that dropped the atomic bomb on Hiroshima.

Altogether, Col. Farnum served in the army for 32 years, retiring in 1949. He spent his last three years in the service as a member of the War Decorations Board.

From 1949 to 1959 he was an automobile salesman for Shirlington Motor Co. in Arlington. For the next eight years he served as business manager and treasurer of St. John's Episcopal Church on Lafayette Square in Washington.

Col. Farnum was born in Wichita, Kan., and attended the University of Wisconsin before joining the army during World War One. He lived in Arlington from 1945 to 1971 and since then had lived at Goodwin House in Alexandria. His wife, Louise Foote Farnum, died in 1970.

Surviving are two sons, William Jr., of Campinas, Brazil and William P. McNeel, of Fort Bragg, Calif., a sister, Frances Farnum of Kansas City, Mo., seven grandchildren, and one great-grand children.