A man who was sitting in a car packed in snow on East Capitol Street, apparently waiting for the car windows to defrost, was killed yesterday when the car burst into flames, D.C. homicide detectives said.

The man's identity had not been determined by late yesterday. His body was found on the driver's seat of the car, which was parked in the 1600 block of East Capitol Street.

Homicide detectives speculated that the man lit a cigarette and ignited gas fumes that had escaped from a faulty carburetor or gas line. Because the car was packed in snow, they said, less air may have reached the car to carry off the gas fumes, allowing the fumes to become concentrated.

Witnesses told detectives the man had cleared off snow from the roof and driver's door of the car and then stepped inside the car. The engine had been running for a half hour before the 9 a.m. fire, witnesses told detectives.

The car, a 1978 Pontiac Trans-Am, was registered to a 35-year-old Department of Sanitation employe. Homicide detectives said he may be the victim but were not releasing the name until dental charts had been checked.

The fire began in the front of the car, burning the man's body beyond recognition, homicide detectives said. The door on the driver's side was slightly opened and the man's foot was resting against it, fire officials said.