William Eugene Leishear, 63, a retired special agent with the FBI who also operated a private investigative service in Takoma Park, died of cancer Wednesday at his home in Frederick, Md.

Mr. Leishear was born in Washington. He joined the FBI in 1939 after earning a law degree from the old Columbus University School of Law. He worked in the field before returning here in 1950, when he became a supervisor at FBI headquarters here. He retired in 1965.

Following his retirement, Mr. Leishear established the Business and Professional Security Service in Takoma Park, which he operated until becoming ill about two years ago.

Mr. Leishear had lived in Vienna, Va., and Baltimore before moving to Frederick, Md., in 1971. From 1973 to 1976, he taught firearms training and law enforcement at Frederick Community College. He established the associate of arts program in criminal justice there.

He was a member of St. John's Catholic Church in Frederick and a members of the Society of Former FBI Agents.

Survivors include his wife, Judy Ann, and two sons, Jonathan, and James, of the home in Frederick; three other sons, William E., of Burlington, Wis., John, of Clinton, Md., and Michael, of Laurel, and two daughters, Jean Seering, of Charlottesville, and Dianne Kuhn, of Morgan Hill, Calif.