Arthur Edward Ruark, 79, an authority on nuclear energy and a former high official of the old Atomic Energy Commission, died Tuesday at his home in Washington. He had a cardiovascular disease.

Dr. Ruark joined the AEC, whose functions now are carried on by the Department of Energy, in 1957. He had spent his professional life as a teacher and researcher in nuclear physics and he was named chief of the controlled thermonuclear branch in the research division of the AEC.

His job was to supervise "Project Sherwood," the agency's effort to harness the thermonuclear energy of the hydrogen bomb for peaceful purposes. If this could be done, it would provide a limitless source of energy. The posibilities sometimes gave Dr. Ruark pause.

"Think of it," he said a year after joining the AEC. "All the power the world's population would need for 10 billion years. It's so staggering I have to laugh at my own inability to understand what it means."

In 1961, Dr. Ruark became assistant director of research for the AEC controlled thermonuclear program, and in 1966 became a senior associate director of research. He retired in 1969.

Dr. Ruark was born in Washington and grew up here and in Martinsburg, W. V. He did his undergraduate and graduate work at Johns Hopkins University in Baltimore, where he earned a doctorate in physics in 1924.

He was a member of the atomic structure section of the U.S. Bureau of Standards in Washington from 1922 to 1926. He then taught at Yale University for a year. From 1927 to 1934 he taught and did research in Pittsburgh.

In 1930, he and Dr. Harold C. Urey, a Nobel prize winner, published "Atoms, Molecules and Quanta." The book became a standard text in its field.

From 1934 to 1944, Dr. Ruark was head of the physics department at the University of North Carolina. In 1944, he returned to Washington and worked at the Naval Research Laboratory for the next two years.

In 1946, he renewed his association with Johns Hopkins by joining its Advanced Physics Laboratory, which has its headquarters in Laurel. From 1947 to 1952, he was an official of the Institute for Cooperative Research, another part of Johns Hopkins. From 1953 to 1957, he was a professor of physics at the University of Alabama.

After his retirement from government, Dr. Ruart taught at Montgomery Community College and did consulting work. He maintained a home in Kensington as well as one in Washington.

Dr. Ruark's wife, the former Sarah Grace Hazen, whom he married in 1927, died in 1967.

Survivors include four daughters, the Rev. Dr. Annette Ruark, of Staten Island, N.Y., Helen van Laer of New York City, Mary Lee Fennel of Kensington, and Patricia Obert of Pasadena, Md.; two brothers, Robert G., of Ridgewood, N.J., and Eric S., of Baltimore, and seven grandchildren.