Col. John Paul Stapp, an Air Force medical researcher who rode a rocket-powered sled at a speed faster than a .45-caliber bullet in an experiment to test the limits of human endurance, died on Saturday at his home in Alamogordo, N.M. He was 89.

Dr. Stapp was known as the ''fastest man on earth'' for his 1954 ride, though the speed has since been surpassed and was never accepted by auto racing officials as an official land speed record. The speed was impressive, at any rate. Dr. Stapp accelerated in 5 seconds from a standstill to 632 miles an hour. The sled then decelerated to a dead stop in 1.4 seconds, subjecting Dr. Stapp to pressures 40 times the pull of gravity.

He became an immediate celebrity. The New York Herald Tribune called him ''a gentleman who can stop on a dime and give you 10 cents change.''

He won what will perhaps be even more lasting fame in a test five years earlier, when he suffered injuries owing to a mistake by a Captain Murphy. The result: Murphy's Law.