James R. (Nature Boy) Williams, 50, a former first baseman for the Indianapolis Clowns baseball club and a retired chauffeur for the Admiral Limousine Service here, died Tuesday at Southern Maryland Hospital Center in Clinton after a heart attack.

Mr. Williams played with the Clowns, baseball's equivalent of the Harlem Globetrotters, from 1952 to 1966. Founded in 1929, the team became part of the Negro American League in 1942 and played to record-breaking crowds in 40 states and Canada and were booked into most major-league stadiums and virtually every minor-league city. A former teammate of Mr. Williams', Hank Aaron, was sold by the Clowns to the old Boston Braves organization in 1952.

The Indianapolis Clowns moved to Cincinnati in the early 1970s.

Mr. Williams, who was born in Rome, Ga., had made his home in the Washington area since the early 1950s. He lived in Oxon Hill.

He was a banquet manager and head waiter for the Sheraton and Marriott corporations before joining Admiral Limousine Service in about 1977. He retired earlier this year for health reasons.

Mr. Williams was a member of the Arlington Divot and Golf Club.

He served in the Army for four years in the late 1940s.

Survivors include his wife, the former Freda Conner, and a step-son, Francis (Buck) Bucklew, both of Oxon Hill; five brothers, Columbus, Elmo, and Edward C., all of Chicago, David, of Indianapolis, Ind., and Hudson (Hug), of Cleveland, Ohio; four sisters, Clara McClure, Mary Haney and Renetha Juniors, all of Indianapolis, and Dorothy Chatman of Chicago, and four grandchildren.