Joseph F. Worley Jr., 51, a research plant pathologist with the Department of Agriculture's plant hormone and regulators laboratory in Beltsville, died Thursday at Suburban Hospital in Bethesda after a heart attack.

A specialist in microscopy, Dr. Worley's early work on the translocation of viruses in plants helped explain how these diseases spread. He also was instrumental in describing a new type of microorganism, spiroplasma, which was associated with many plant diseases.

More recently, he had the primary responsibility for discovering and describing biological activity of natural products that regulate plant growth.

Dr. Worley was the author of coauthor of more than 60 scientific publications.

He joined Agriculture's Beltsville Research Center in 1965, while earning a doctorate in botany from George Washington University. He also earned bachelor's and master's degrees there.

Dr. Worley was born in Washington and graduated from Western High School. He served as a medic with an Army mobile dental unit in Germany in the early 1950s.

He lived in Rockville and was a member of the First Baptist Church in Washington.

Survivors include his wife, Anita S., of Rockville; his father, Joseph F. Sr., of Silver Spring, and a sister, Barbara W. Porter of Nashville, Tenn.

The family suggests that expressions of sympathy be in the form of contributions to the American Heart Association.