Wilbur Magruder Hurst, 81, a retired section chief in the Department of Agriculture's Agricultural Engineering Research Division, died Friday at Holy Cross Hospital of Silver Spring. He had a heart ailment.

An agricultural engineer and fiber specialist, Mr. Hurst was a leader in machinery developments that helped modernize the fiber flax industry in the Pacific Northwest.

He joined Agriculture in 1937. During World War II, he was in charge of fiber flax investigations at Corvallis, Ore., and later assisted in a cooperative project between the Agriculture Department and the Cuban government in processing jute substitute fibers.

In 1945, he transferred to Agriculture's Beltsville station, where he conducted a research project to improve engineering and other technical aspects of cooperative farming and rural industry. He held patents on three engineering devices dedicated to public use that were developed in association with this project.

Mr. Hurst was made head of the USDA's cotton ginning section in 1952, where he was largely responsible for making fiber quality testing an integral part of investigations for improved ginning. He retired in 1960. He was a resident of Silver Spring.

He was born in Morton, Miss., and served in the Navy during World War I. He earned a bachelor's degree in agriculture from Mississippi State College in 1923 and a bachelor's degree in agricultural engineering from Iowa State College in 1925.

Survivors include his wife of 52 years, Ruth P., of Silver Spring; three daughters, Dona Serakos of Minneapolis, Sarah Lou Johnson of Springfield, and Ann Goldstein of Washington; seven grandchildren and a great-granddaughter.

The family suggests that expressions of sympathy be in the form of contributions to a charity of one's choice.