Edward Elliot Sinclair, 54, an official of the Energy Research and Development Administration, died Monday after apparently suffering a heart attack at his office in Germantown.

At the time of his death, he was special assistant to the director of the reactor research and development division.

Born in Cambridge, Mass., Dr. Sinclair received bachelor's and master's degrees from Clark University in Worcester. In 1944 he began work as a chemist with the Manhattan Engineering District at Oak Ridge, Tenn., working in analytical chemistry of uranium.

From 1956 to 1959 he was the AEC scientific representative to Canada, stationed at the Canada Atomic Energy Project at Chalk River, Ont.

Dr. Sinclair then was named assistant director for technical implementation in the AEC's division of international affairs. In 1961, he became assistant director for nuclear technology, division of reactor development AEC.

He became special assistant in reactor research and development activities in 1973, and continued in the position when AEC was incorporated into ERDA in 1975.

Dr. Sinclair participated in the Third United Nations International Conference on Peaceful Uses of Atomic Energy in Geneva in 1969.

He is survived by his wife, Nancy Carol Sinclair, and a son, Jonathan, of the home in Derwood, Md.; four other children, David, of South Carolina, Deborah, of Gaithersburg, Susan, of Orlando, Fla., and Vanessa, of Silver Spring, and a brother, Fred, of Massachusetts.

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