Clarence G. Donovan, 86, a retired chemist and former head of the Pesticide Regulation Division laboratory, U.S. Department of Agriculture, died Thursday at Sibley Memorial Hospital. He had a heart ailment.

Mr. Donovan, who lived in Washington, joined the division in 1930 and became chief of its chemical laboratory in 1947. He was named head of the division's case development section in 1961. He retired two year later.

During his tenure, Mr. Donovan had developed a number of methods for chemical analysis of pesticides which eventually were used in laboratories throughout the world.

He was born in Washington and graduated from old Western High School and the University of Maryland. In 1917, he worked briefly as a chemist for the Pennsylvania Railroad in Altoona, Pa., served in the army during World War I, and then returned to the railroad. He remained there until joining the Agriculture Department here.

Mr. Donovan was a member of the Izaak Walton League, the American Legion and the Holy Name Society of St. Ann's Catholic Church.

He is survived by his wife of 58 years, Ethal A., of Washington; two daughters, Marianne D. Doran of Tucson, Ariz., and Carolyn Spain of Silver Spring, eight grandchildren and eight great-grandchildren.