A 27-year-old city man died of injuries he suffered last night when the motorcycle he was riding crashed into the cab of a tractor-trailer on the Southwest Cutoff section of Route 20, officials said.

Andrew Belsito was pronounced dead at UMass Memorial Medical Center - University Campus, police Sgt. Donald A. LaRange of the Traffic Division said. Mr. Belsito suffered serious leg injuries. Medical personnel had recovered part of his leg at the crash scene, investigators said.

Witnesses told police Mr. Belsito was traveling east very fast and was doing a wheelie when his Yamaha motorcycle slammed into the truck.

The sergeant said Joshua Roy, 27, of East Brookfield, driver of a tractor-trailer for Sturbridge Service Center, was pulling out of the service center yard to go west on Route 20 when Mr. Belsito's motorcycle collided with the diesel fuel tank on the truck's left side. About 50 gallons of fuel spilled onto the road. It was cleaned up by Corporate Environmental Advisors, police said.

Sgt. LaRange said Mr. Roy never saw the motorcyclist's headlight because it was pointed at the sky during the wheelie.

The accident occurred at 6:15 in front of the service center and across the road from the 99 Restaurant. Eastbound traffic was rerouted to Route 122, police said.

Sgt. LaRange said the fatality is being investigated by Officers George M. Kelly and William J. Armstrong of the Traffic Division and the state police truck team.