Three persons were killed yesterday evening in a fiery chain-reaction collision that occurred when a Trailways bus struck the rear of their car, which had halted in heavy rush-hour traffic on Rte.I-95 near the Capital Beltway in Prince George's County, Maryland State Police reported.

The approximately 30 passengers aboard the bus, which was bound for Silver Spring and Washington, all escaped before the vehicle was gutted by flames. Fire also engulfed the twisted, crumpled metal wreckage of the car in which the three victims had been riding and left their bodies burned beyond recognition. Another car was also burned, and billowing clouds of smoke were visible for miles.

A total of four cars, all ahead of the bus in the southbound lanes of I-95, were involved in the crash, which tied up traffic for miles around long into the night. At least three persons were reported injured in the collision, which occurred about 6 p.m. Neither was described as seriously hurt.

State police Sgt. William L. Moberly said the four cars were stopped in the extrene right hand lane because of a backup at the exit ramp leading to the Beltway and Silver Spring. He said the bus failed to stop and struck the car ahead, causing the chain of collisions.

The three dead were listed as Catherine Amelia Wehr, 46, of 1120 Reese Rd., Severn, Md., David Wayne Jacobs, 15, of the Reese Road address, and the woman's son, Robert Allen Wehr, 13, of Wlakersville, Md.

One of the bus passengers, a 63-year-old man said: "We heard a boom and looked up and saw flames [outside the bus] like a molotov cocktail."

The man, who declined to be named, said that after leaving the bus, he and the bus driver helped pull a woman from a burning car directly in front of the one in which the three died. The rescued woman was identified last night as Kathy Rogers of Sterling, Va.

Margo Moyer of Roanoke was asleep in a fifth-row bus seat when the collision occurred.

"I felt a lurch and it woke me up," she told a reporter last night. She said evacuation of the bus was orderly but some passengers were bruised in escaping. Some left through windows.

Roberta Dawson of Charlottesville, who also was seated near the front of the bus, said she heard a muffled report like the sound of a tire blowout just before the collision, which jolted her and caused her to bite her lip.

It was several hours before authorities were able to identify the dead, who apparently had been killed on impact. Identificaiton was made through a wallet that was found in the car.

"They were completely crushed," said Chief John Coleman of the Beltsville Volunteer Fire Department.

Both the front and the rear of the car in which the three died were smashed. The second car, from which the woman was pulled, lay on its side in the roadway, about a dozen feet in front of the victims' car.

About 100 feet in front of the first two cars was a third car that also had apparently been struck in the rear. A fourth car, also believed involved in the collision, was on the shoulder of the road.

Two of the injured were taken to Holy Cross Hospital. One was believed to be a bus passenger. The third, the rescued woman, was taken to Prince George's General Hospital, with facial cuts. She was in stable condition.

An official at the Trailways station in Silver Spring said the bus left New York for Washington at 1 p.m. It stopped at Baltimore at 4:40 p.m. and at Laurel at 5:15, the official said. It was due at Silver Spring at 5:45 p.m. and in Washington 30 minutes later.