John A. Kennedy Jr., 51, a Washington attorney who had practiced international trade law for more than 20 years and was an adjunct professor at the Georgetown University law school from 1966 to 1971, died Sept. 25 in George Washington University Hospital after a stroke. He lived in Chevy Chase.

Mr. Kennedy was born in California and reared in Washington. He was a 1949 graduate of Gonzaga College High School, and graduated summa cum laude from Georgetown University in 1953. He was a Fulbright scholar at the London School of Economics and served with Army intelligence in Europe before graduating from Harvard University law school in 1959.

He was a fellow of the Institute for International and Foreign Trade Law at Georgetown University law school in 1960. He had been legal counsel for the Japan-America Society.

He was a partner in the old Washington firm of Stitt, Hemmendinger & Kennedy, and at the time of his death was a partner in the firm of Arter, Hadden & Hemmendinger in Washington.

Survivors include his wife, Dr. Marie-Louise Levy Kennedy of Chevy Chase; a daughter, Leigh J. Kennedy, also of Chevy Chase, and his parents, Dr. and Mrs. John A. Kennedy Sr. of Silver Spring.