John Albert Stevenson, 89, retired head of the division of mycology and disease survey of the Agriculture Department, died Tuesday at the Sleepy Hollow Nursing Home after a stroke.

As head of the division, he was in charge of research on the identification of fungi that cause plant diseases. He retired in 1960, but continued to work as a collaborator in the department for another 15 years.

Mr. stevenson came to Washington in 1918 as a pathology inspector with the Federal Horticultural Board. He later was in charge of foreign agricultural explorations and then became a mycologist in 1927.

Mr. Stevenson, who was the author of two technical books and more than 100 articles, was an honorary curator of fungi in the botany department of the Smithsonian Institution.

In 1976, he presented his mycological library of more than 6,000 volumes to the Smithsonian with the understanding that it remain part of the National Fungus Collections at the Agriculture Department's Beltsville quarters.

Mr. Stevenson was born in Woonsocket, S.D. He grew up in Bayfield, Wis. and Sioux City, Iowa. He earned a degree in forestry from the University of Minnesota and studied plant pathology and ecology.

He was a plant pathologist in Puerto Rico for several years before coming to Washington.

He received a number of awards during his career, including the Agriculture Department's Superior Service Award.

Mr. Stevenson was a charter member and past president of the Mycology Society of America and past president of the Botanical Society of Washington. He had held executive positions with the Washington Academy of Sciences and the American Phytopathological Society and belonged to a dozen other scientific organizations in this country and abroad.

He was past master of the William B. Singleton Masonic Lodge in Washington.

He is survived by his wife, Katherine T., of the home in Falls Church; three sons, John A. Jr., of Falls Church, Robert, of Alexandria, and Donald, of Concord, Mass.; a sister, Mary French, of Saint Petersburg, Fla., eight grandchildren and four great-grandchildren.