ST. LOUIS (AP) _ Police said they planned to seek manslaughter charges today against the driver of a school bus that crashed while allegedly racing with a car, killing one student and critically injuring a second.

Detective Sgt. Fred Fone said warrants would be sought against Mark Trice, 26. Investigators said the bus went out of control Monday on Interstate 70, hit a guard rail and smashed into a steel pole, ripping the passenger compartment from the frame.

Witnesses said the dead girl, Kimberly L. Bogan, 18, had to be pried from the wreckage of the bus, which was carrying 13 students from Parkway North Senior High School to their homes in north St. Louis.

''People were lying all over the side of the highway,'' said John Otte, chief of the Normandy Fire Protection District. ''I have seen school buses in other accidents, school buses on fire, but nothing like this.''

Trice and 12 other students were injured in the crash. Cynthia Alexander, 15, was reported in critical condition today with head injuries. Most of the other injuries were minor, authorities said.

Fone said several students who were sitting in the front of the bus told them that Trice acted as though he was racing with a small car when he apparently swerved toward it to scare its driver and lost control of the bus.

According to Fone, some students told investigators that before the crash Trice asked, 'Should we cut him (the driver of the car) off?'''

One student, Joyce Jones, 14, said Trice was driving erratically for most of the ride. She said Trice ''started racing a car, a green Volkswagen, and he said, 'Do you want me to run him over?'''

''He started swerving into another lane,'' she said. ''We were just playing around and at first we say, 'Yeah, go ahead.' But when he did it, we said, 'Stop it.' He didn't have control. He was driving real fast.''

But Lee Collins, a brother of Trice and a driver for the same bus company, said Trice ''told me he was telling the kids to sit down. He looked around to tell them that, and to avoid hitting the Volkswagen, he swerved. That's when he hit whatever he hit.''

Fone said Trice, who was reported in stable condition, had refused to take a breath test for alcohol, but that police had obtained a warrant for a blood test for alcohol and drugs.

''But no matter what that result is, we will seek a warrant (for vehicular manslaughter),'' Fone said.

Officials said Trice, Bogan and five other students were taken to Normandy Osteopathic North Hospital. Seven other students, none of them seriously injured, were taken to another hospital for treatment.

Fone said witnesses told them the bus had been traveling at high speed and had been weaving through traffic for some time before the crash.

A spokesman for the bus company, R.W. Harmon & Sons, which has a state contract to transport students under the desegregation program, declined to comment on the crash, saying it was under investigation. He said Trice appeared to have a clean record. Police said, however, that he had several speeding charges on his record.

The accident closed the eastbound lanes of I-70 for about two hours during rush hour, causing a massive traffic jam.

Fone said police are also seeking the driver of the Volkswagen that had been alongside the bus. But he said he did not believe the driver of the car had intended to race the bus.

School officials said it was the first fatal school bus accident in the five-year history of the desegregation program.