Galen Miller Yates, 65, a retired trade fair manager for the Agriculture Department's Foreign Agricultural Service, died Sunday at Fairfax Hospital of pneumonia and polymyositis, a disease of the connective tissue. He lived in Fairfax.

Mr. Yates began his 40-year government career with the General Services Administration's Procurement Division. He also worked at the Naval Observatory here before transferring to Agriculture in 1944. He served as trade fair manager from 1964 until his retirement in 1974 and was responsible for developing overseas markets for U.S. agricultural products.

Besides his government career, Mr. Yates tuned pianos and worked as a real estate broker in Northern Virginia.

Born and reared in Washington, he graduated from McKinley High School. He earned his bachelor's degree from the Strayer College School of Accountancy.

Mr. Yates was a longtime member of the Washington City Church of the Brethren here and served as the church's minister of music for 20 years.

Survivors include his wife, the former Gloria Godfrey, and two daughters, Carolyn Seidel and Gayle McKendree, all of Fairfax; another daughter, Jean Browne of Arlington; a brother, Cecil R., of Oxford, Md., and eight grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to Compassion International, P.O. Box 7000, Colorado Springs, Colo., 80933, or to the Muscular Dystrophy Association.