Seymour H. Smiley, 56, deputy director of the office of nuclear material safety and safeguards of the Nuclear Regulatory Commission, died in Atlantic City, N.J., Saturday following a heart attack.

Mr. Smiley was stricken while jogging on the Atlantic City boardwalk. He and his wife, Ruth, had gone to the resort to attend a religiouss education meeting.

Mr. Smiley was born in New York and began his career in nuclear energy in 1943 after graduating from New York University with bachelor's and master's degrees in chemistry.

He was assigned to the Manhatten Project, which developed the first atomic bomb, and the transferred to the nuclear energy facility at Oak Ridge, Tenn. He worked on the gaseous diffusion process of uranium enrichment at Oak Ridge and became superintendent of engineering and reprocessing at the facility's gaseous diffusion plant in 1953. In 1967, he entered private industry in Pittsburgh, where he continnued to work on nuclear energy.

In 1971, he moved to the Washington area and joined the regulatory staff of the ald Atomic Energy Com- for fuels and materials licensing. The mission, where he was deputy director regulatory arm of the AEC was designated the Nuclear Regulatory Commission, an independent agency, by the Energy Reorganization Act of 1975.

Mr. Smiley held several patients on the gaseous diffusion process of uranium enrichment. He also was the author of more than 200 articles on the subject and had been a guest lecturer at the Massachusetts Institute of Technology and at the University of California.

In addition to his wife, of the home in Bethesda, survivors include a son, Jeffrey, of Germantown, Md.; a daughter, Sherry, of Bethesda, and his parents, Mr. and Mrs. Benjamin Smiley, of Hollywood, Fla.