A Prince George's County school bus filled with students swerved to avoid hitting a car on the Baltimore-Washington Parkway yesterday morning, then overturned, tumbling first onto its right side and then to its left, and sending all 48 students to three hospitals, police said.

Officials said that most of the injuries were limited to scrapes, cuts and bruises on the students, who were bound for Fairmont Heights High School. Two of the students remained hospitalized for observation last night at the Washington Hospital Center, police said.

The accident occurred about 8:15 a.m. as the bus headed south on the parkway, U.S. Park Police said, just north of the fork in the road at New York and Kenilworth avenues.

The bus was traveling in the center lane when a 1981 Toyota switched from the right lane in front of the bus, said Maj. Richard Cusick of the park police. The bus driver braked, police said, and swerved to avoid hitting the Toyota. The bus flipped on its right side, he said, slid several feet in the left lane, hit a curb and flipped over onto its left side. Books, papers, purses, clothing, shoes and seat cushions scattered throughout the bus, students said.

The bus driver, Lenora Simmons, 44, was not injured. School spokesman Brian Porter said Simmons, who has been a driver for 12 years, has a clean driving record and was rated "very good, very skillful" on her last evaluation. Cusick of the park police said the bus apparently was going within the 45 mph speed limit.

Park Police said the driver of the Toyota, Mary Hemingway of College Park, was charged with making an unsafe lane change.

"The bus just started tumbling and tumbling and tumbling," said Tanya Penny, 15, a 10th grader at the school, who was seated near the rear of the bus. "I thought the bus was going to explode."

The front window of the bus popped out in one piece, as the shatterproof glass is designed to do, school officials said, and two rear windows broke. Some students climbed out of the bus through the front window, school officials said, and others used the rear emergency exit.

"It was hysterical," said Angela Cromartie, 16, an 11th grader at the school. "Everybody was on top of each other, screaming, trying to get out, trying not to get hurt."

The accident occurred about one mile from Prince George's General Hospital, where 21 of the 48 students were taken. Twenty-five other students were taken to AMI Doctors' Hospital in Lanham. Both hospitals' emergency rooms called in extra staff to handle the large number of victims, who were transported by Prince George's and District of Columbia ambulances.

Two students, Antoinette Flint, 18, and Tanya Smith, 18, were taken by Park Police helicopter to the Washington Hospital Center. Both were still hospitalized last night and listed in fair condition.

News of the accident brought parents rushing to the hospital emergency rooms.

Antoinette Flint's mother, Phyllis Flint, was at her Landover Hills home about 9 a.m. when a knock at the door interrupted her laundry chores. It was her 17-year-old son Robert, who had left for school on the bus with Antoinette an hour earlier, accompanied by a school friend and an off-duty police officer.

Robert broke the news to his mother. "Mom, there's been a bus accident," she recalled his saying in a shaky voice. "Antoinette was taken to the hospital by helicopter."

Phyllis Flint said her knees suddenly felt weak and she thought she would collapse. "I was stunned," she said. "In the back of my mind was the worst."

She headed for the closest hospital, Prince George's General, but her daughter was not there. An hour later, a hospital employe told Phyllis Flint that her daughter had been taken to the Washington Hospital Center. Phyllis Flint said she prayed during the car trip to the second hospital and felt relieved when doctors there told her that Antoinette had suffered only minor scrapes and bruises. When she finally saw her daughter, she cried.

"I thanked almighty God she was all right," she said, as she wiped away the tears streaming down her cheeks. "Those kids could have been killed."