Donald L. Mckernan, 61, a marine biologist and head of the Department of State's office of ocean affairs here during 1966-74, died of a heart attack Wednesday while on a trade mission in Peking, China.

He was a member of a delegation of the Washington State Council on International Trade now touring the Far East.

Mr. McKernan came here in 1957 when he was appointed the first director of the Department of the Interior's Bureau of Commercial Fisheries. In 1966 he became a special assistant to the secretary of State and coordinator of ocean affairs for the State Department, during which time he held the rank of special ambassador.

He began his career in marine biology in 1941 with the state of Washington's Department of Fisheries. He subsequently worked for Interior in Honolulu and was administrator of commercial fisheries in Alaska for the U.S. Fish and Wildlife Service.

In 1974, after leaving the State Department, he became a professor of marine affairs and fisheries and director of the Institute for Marine Studies at the University of Washington in Seattle.

Mr. McKernan was born in Eugene, Ore., and grew up in Seattle. He graduated from the University of Washington.

He served as commissioner of the International North Pacific Fish Commission during 1972-74. He also was commissioner of the Northwest Atlantic Fish Commissioner in 1974 and commissioner of the U.S. Canadian Great Lakes Fisheries Commission during 1960-66.

He was a U.S. delegate to the United Nations Law of the Sea Conference for many years and at the time of his death was chairman of the National Advisory Committee on Oceans and Atmosphere. He also was a consultant to the National Academy of Sciences.

Mr. McKernan had published numerous scientific papers in hid McKernan had published numerous scientific papers in hisService Award and the State Department's Distinguished Honor Award.

Survivors include his wife, Patricia, of the home in Seattle; five daughters, Barbara Rintamaa, of Adrian, Mich., Rebecca Fredere, of Cincinnati, Cathy Osborne, of Cleveland, Debra Ragan, of Virginia Beach, Va., and Cynthia, of Tacoma, Wash.; two brothers, Clyde R., of Seattle, and Ralph, of Eugene, and nine grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Children's Orthopedic Hospital and Medical Center in Seattle or to the American Heart Association.