Primo Nebiolo, the most powerful man in track and field and one of the most powerful figures in world sports, died at a Rome hospital early yesterday morning after a heart attack. He was 76.

Nebiolo, president of the International Amateur Athletic Federation since 1981, led track and field into its lucrative modern age with a fiercely independent style that generated many detractors. A former long jumper who headed several businesses in Italy, Nebiolo took the IAAF from a $50,000-a-year operation that depended on amateur athletes to a $40 million business that flaunted its highly paid superstars.

His death "creates great uncertainty about the short- and long-term future of track and field," USA Track and Field CEO Craig Masback said. "His legacy will be that of having ushered track and field from an amateur era to its professional era. . . . If there is not a person of similar vision and power to step up, it's going to be a significant loss."

IAAF Vice President Lamine Diack of Senegal will succeed Nebiolo on an interim basis. The IAAF is expected to determine how to elect a successor at its Nov. 18-19 meetings in Monaco.

Nebiolo, who will be buried Tuesday, created the Golden League circuit in Europe, approved prize money at the world championships beginning in 1997, and earned a reputation for living a luxurious life that kept pace with his innovations.

He frequently butted heads with the International Olympic Committee and Olympic Games organizing committees over revenue for international federations, Olympic Games tickets, television issues and drug-testing matters.

Still, IOC President Juan Antonio Samaranch called Nebiolo "one of the greatest leading sportsmen of this century, who knew how to elevate the sport to the place it deserved in contemporary society."