Robert D. Schamberger, 56, a nuclear physicist with the Nuclear Regulatory Commission, died of cancer Friday at Suburban Hospital in Bethesda. He lived in Gaithersburg.

Dr. Schamberger had been with the NRC since 1974. His latest assignment had been with a special group investigating the problems at Three Mile Island, which made a study over a period of six months last year.

He was chief of the experimental, gas-cooled reactor safety branch at the NRC.

Dr. Schamberger was born in Schenectady, N.Y. A graduate of Union College there, he earned a doctorate in nuclear physics from the University of Rochester in New York.

From 1951 to 1956, he worked at the Brookhaven National Laboratory on Long Island, N.Y. He then spent two years as supervisory physicist at the Aeronautical Research Laboratory, Wright Air Development Center, in Brookhaven.

Dr. Schamberger worked from 1958 to 1974 for the Gulf Nuclear Fuels Co. and its predecessors at Pawling, N.Y., and Elmsford, N.Y., where he was manager of the physics and mathematics department.

He was a member of the American Physical Society, the American Nuclear Society and the American Association for the Advancement of Science.

He is survived by his wife, the former Shirley Smith, of Gaithersburg; a son, Robert D. Jr., of Ithaca, N.Y.; three daughters, Lynn, of Wappingers Falls, N.Y., and Dale Kogler and Kay Wilke, both of Rochester; his mother, Eldora Schamberger, of Loudenville, N.Y.; a brother, John M., of Newington, Conn.; a sister, Barbara Cornett of Lynchburg, Va., and three grandchildren.