J.F. Gates Clarke, 85, a leading authority on moths and the former chairman of the department of entomology at the Smithsonian Institution's Museum of Natural History, died of heart ailments Sept. 17 at his home in Hyattsville.

Dr. Clarke joined the staff of the Smithsonian Institution in 1954 as a curator in the division of insects. He was chairman of the department of entomology from 1963 to 1965, senior entomologist from 1965 to 1975 and research associate from 1976 until his death.

His work included investigations of how moths and other insects colonize in the island chains of the Pacific. As part of this study, he traveled to Borneo, Tahiti and the Marquesas Islands and brought back specimens that helped make the Smithsonian's collection of Pacific moths one of the finest in the world.

Dr. Clarke also was instrumental in building the Smithsonian entomology department's collection of more than 30 million moths.

He was the author of 102 research papers; a guide book, "A Golden Book of Butterflies"; and a 4,000-page basic reference book on the taxonomy of lepidoptera worldwide. His most recent publication was a study of the small moths of the Marquesas, published in 1986.

A native of Victoria, B.C., Dr. Clarke moved to Bellingham, Wash., when he was 11. He graduated from Washington State University with degrees in pharmaceutical chemistry and zoology. He also received a master's degree in entomology at Washington State, where he taught biology from 1931 to 1935.

He moved to Washington and joined the Department of Agriculture as an entomologist in 1935. He served in the Army in Europe during World War II, and was discharged as a captain. He was awarded a Bronze Star.

After the war, Dr. Clarke studied entomology at the University of Paris, then returned to Washington and the Department of Agriculture. While working there, he received a doctorate in entomology from the University of London.

He was a stamp collector and a member of the Cosmos Club.

His wife of 59 years, Thelma Miesen Clarke, died in 1988.

Survivors include his second wife, Nancy duPre Clarke of Hyattsville; two children of his first marriage, J.F. Gates Clarke Jr. of Wilmington, Del., and Carol Clarke Lewis of Frederick, Md.; five grandchildren; and a great-grandson.