William R. Porter Sr., 39, the supervisor of the audio-visual staff at the Museum of History and Technology of the Smithsonian Institution, was killed Thursday in a motorcycle accident in Charles County, Md.

The Charles County sheriff's office said the motorcycle Mr. Porter was riding ran out of control on Route 227 about eight miles west of Waldorf, struck a ditch, turned over several times, and then struck a utility pole. Officials said Mr. Porter was pronounced dead on arrival at Physicians Memorial Hospital in LaPlata.

As supervisor of the audio-visual staff at History and Technology, Mr. Porter designed and installed equipment for use with the museum's exhibits. He also installed equipment for use during lectures, concerts and similar events. He had joined the Museum in 1970.

Mr. Porter was born in Springhill, Pa. He enlisted in the Navy in 1957 and became an electronic technician and television operator. He helped make training films at the Naval Photographic Center in Washington and later served as the electronic shop supervisor aboard the U.S.S. Steinaker.

He moved to the Washington area in 1963, the year he left the Navy, and spent the next seven years as an electronics technician at the General Services Administration.

Survivors include his wife, Cynthia, and two sons, William R. Jr. and John Scott, all of the home in Waldorf.