Barbara Mary Bisset, 31, a legislative assistant in the executive offices of the United States Railway Association here, accidentally drowned Sunday while swimming in the ocean at Cape Hatteras, N.C.

Friends said Miss Bisset, who was proficient at swimming as well as water and snow, skiing, parachuting, scuba diving and tennis, was spending the weekend at Cape Hatteras. She lived in Alexandria.

She was born in Hampstead, North London, England, and studied secretarial work at Roke Secondary Modern School in England.

She came to Washington in 1968 and worked as an editorial secretary at the old Washington Daily News until it was purchased by The Washington Star in 1972. She then was a secretary assistamt to the president of the National Ocean Industries Association until joining the Railway Association in 1974.

Miss Bisset was a member of the Ski Club of Washington, the Love Set Tennis Club, the Skyline Tennis and Racquet Club, the Ski and Dive scuba club of Alexandria and Johnnie's Gang, a Group devoted to outdoor activities. She had parachuted with the group and was in training for an upcoming show in Vienna. Va.

She is survived by her mother, Christina Bisset; two brothers, George and Robert, and a sister, Dorothy Ross-Champkins, all of Surrey, England.