Mr. Byrd's family described him as a resident of the affluent Beacon Hill section of Boston.

His son, Leverett Byrd of Needham, Mass., was quoted in The Baltimore Sun yesterday as saying that Mr. Byrd left Boston on Sept. 13 to attend a ceremony at the Washington headquarters of the National Geographic Society. The ceremony honored his father, Adm. Richard E. Byrd, the pioneer aviator and polar explorer, who achieved fame with his long-distance flights over the Arctic and expeditions in Antarctica from 1924 to 1956.

''I put him on a train, and my wife was supposed to meet him,'' Leverett Byrd said. ''What happened in between, I don't know. It's very strange, this whole thing. We're trying to come to grips with it.''

''He idolized his father,'' Leverett Byrd said. ''The main focus of his life was to continue what my grandfather had started, to help people who wanted information about him.'' Familiar Leitmotif

The face and name of Richard E. Byrd Jr. were a familiar leitmotif in the dashing career of his father. For instance, one day in June 1930, as Mayor Jimmy Walker and crowds of other New Yorkers prepared to welcome Admiral Byrd back from an Antarctic expedition with a hero's parade, they watched the admiral's wife and son waiting at dockside. The New York Times reported, ''Richard Byrd Jr., wide-eyed and eager to meet his long-absent dad, stood beside her, trembling with excitment.''

Admiral Byrd died in 1957. Richard Jr. was born in Boston, attended the Milton Academy and Harvard, joined the Navy and served as an officer in the Pacific during World War II. In 1948, he married Emily Saltonstall, the daughter of Senator Leverett Saltonstall of Massachusetts. They had four children and were divorced in 1960.