Retired Army Maj. Gen. Willis S. Matthews, 76, whose 39-year military career included service as executive officer to General of the Army Omar N. Bradley when Bradley served as the nation's first chairman of the Joint Chiefs of Staff, died Sunday of a heart attack.

He lived in Chevy Chase and was stricken while walking in Washington. He was pronounced dead at the Office of the D.C. Medical Examiner.

Gen. Matthews, who was born in Jackson, Tenn., graduated from the U.S. Military Academy at West Point in 1927. His assignments prior to World War II included various posts in the United States and in the Philippines. During the war, he held several high staff positions in the Pacific.

After the war, he served as Bradley's executive officer for five years. He later served in Germany and at NATO headquarters in France, commanded the 1st Infantry Division at Fort Riley, Kan., and then, in the late 1950s, the U.S. Military Assistance Group in Korea.

His last assignment was deputy commanding general of the First Army with headquarters at Governor's Island, N.Y. He retired in 1963.

For the next two years, Gen. Matthews worked for the New York World's Fair. In 1965, he moved to Chevy Chase and worked for the Research Analysis Corporation in McLean. He retired from that firm about 10 years ago.

Gen. Matthews' military decorations included the Distinguished Service Medal and the Bronze Star.

He was a 32nd degree Mason and a member of the Army & Navy Club, the West Point Society of D.C., and the University Club in New York.

Survivors include his wife, Eugenia Phillips Matthews of Chevy Chase; one daughter, Mrs. John G. Middleton of Rumson, N.J., and three grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the American Cancer Society.