A 17-year-old Fairfax County youth died late Thursday in a fiery automobile crash near Fort Belvoir after he was trapped inside a car that swerved out of control on a winding county road and slammed into a bridge abutment, police said.

The driver of the car, another 17-year-old Fairfax County youth, was charged with involuntary manslaughter and driving while intoxicated, county officials said yesterday.

Theodore J. Garcia, of 3950 El Camino Place in the Mount Vernon area, was killed when a small sports car in which he was riding smashed into the bridge while traveling at speeds police said may have reached 100 mph. The car exploded into flames when it hit the bridge support on Beulah Street west of the Army post.

The driver and another passenger escaped with minor cuts and burns, but Garcia remained trapped in the back seat of the Alfa Romeo, police said. The other passenger, Tracy M. Ferguson, 16, of 4335 Lawrence St. in the Mount Vernon area, and the driver were treated at nearby DeWitt Army Hospital and released.

Deputy commonwealth's attorney V. Britt Richardson Jr. said he authorized involuntary manslaughter charges yesterday "based on the number of violations of the law" allegedly involved in the accident. The driver's name was withheld because he is considered a juvenile under Virginia law.

Police said they believe the three teen-agers had been celebrating the completion of high school examinations.

A Fairfax patrol officer first noticed the Alfa Romeo closely following another car on Beulah Street about 10:45 p.m. Thursday, police said. When the sports car tried to pass another car at high speed, the officer began following, police said.

"When the officer attempted to stop him, the driver accelerated to speeds believed at times to exceed 100 miles per hour," said a police spokesman. "The patrol car couldn't keep up -- it was left in the dust."

Moments later, the police officer topped a hill on the winding road and spotted the sports car in flames at the foot of a railroad bridge near the intersection of Backlick Road, police said.

"The car was gutted," said police spokesman Warren Carmichael, who arrived at the scene minutes after the crash. "It was not even possible to tell what make of car it was from the physical remains." The car was identified by the police officer who had pursued it.

Police said the driver apparently panicked when he approached the arched railroad bridge supports that straddle the narrow road. Police said they believe he slammed on the car's brakes, causing the car to skid about 300 feet before smashing into an abutment and bursting into flames.