Five persons were killed and 12 injured yesterday when a bus taking them to the race track at Charles Town, W.Va., skidded on a rain-slick roadway and smashed into a concrete guardrail on an I-70 highway bridge outside Frederick, Md. Three of the injured were in critical condition.

The bus left downtown Baltimore about an hour before the 12:40 p.m. accident, and all 17 persons aboard were believed from the Baltimore area.

According to Maryland State Police, the initial impact of the crash smashed a section of the guardrail, ripped open the front of the bus, and flung two occupants out of the vehicle and down an embankment to the edge of the Monocacy River more than 80 feet below. Both were killed.

The battered vehicle caromed from the railing and zigzagged wildly across the two-lane westbound bridge, police and witnesses said. Before it finally halted, windows were smashed, seats were torn loose and shouting and screaming passengers tumbled onto the roadway.

A few witnesses said they believed the bus had rolled over or skidded on its side after striking the guardrail. Several described the roadway as a scene of grisly carnage.

"It was pitiful," said Thurman O'Neal, 59, of Baltimore, one of the survivors. "All that blood . . . ," he said. "I couldn't tell who was dead and who was alive."

"All I remember was people screaming," said Mary Colson, 53, of Baltimore, another survivor.

The roadway was smeared with blood and littered with the passengers' belongings and with debris. Dozens of rescue workers arrived quickly, and the westbound lanes of the highway were closed for several hours.

The bus apparently was traveling at "high speed" when the crash occurred, according to Sgt. Bill Tower, a state police spokesman.

However, he said late in the day that investigators still were trying to determine the cause of the accident. "It could be several days before we figure out exactly what happened," he said.

The driver of the bus was thrown down the embankment and was one of the five persons killed, police said. He was identified as George Brown, 68, of Baltimore. Two others killed were identified as Harry Bernstein, 74, of Baltimore and Irvin Myers Sr., 81, of Glen Burnie. Names of the other two dead were withheld pending notification of their relatives.

The bus was operated by the Baltimore Motor Coach Co., which runs regular service to the Charles Town track from Baltimore on racing days. The run of about 70 miles begins at the Civic Center in downtown Baltimore and includes a stop on Rte. 40 near Rolling Road in Catonsville.

Witnesses said most of the passengers boarded at the Civic Center yesterday. About half a dozen were believed to have boarded at the suburban stop.

The silver-colored bus with the red and white trim was about 30 miles northeast of Charles Town yesterday afternoon, traveling through the rain as it approached the bridge over the Monocacy, on the eastern side of Frederick.

The approach leads up a rise, then down an incline. Residents of the area said the bridge can be hazardous in wet weather.

"This bridge can be dangerous going downhill," said Susan Shaw, who lives nearby. "I've lived here about two years, and I still slide on it when I'm driving in the rain."

Mary Colson was seated toward the back of the bus on the left side as the vehicle neared the bridge about a half-hour before the start of the 11-race card at Charles Town.

"I was just sitting there relaxing with my eyes closed when the bus started swaying," she told a reporter in Frederick yesterday.

The bus, she said, "was going too fast for that kind of weather."

Thurman O'Neal, who also received relatively minor injuries, also was seated on the left side of the bus, about five seats behind the driver. He said he too believed the bus may have been traveling too fast.

He told a reporter that the driver braked to avoid hitting a car in front of him. Then, he said, the bus began fishtailing from side to side.

The next few moments, in which the bus struck the concrete railing, were filled with screams and shouts and the smashing of windows, both survivors recalled.

"I was thrown into the aisle," Colson said. " . . . The windows on the side of the bus just fell out . . . . "

O'Neal said that after striking the concrete guardrail, the bus began to roll over, possibly turning over as many as four times before coming to a halt right side up.

However, Tower, the state police spokesman, said last night that investigators could not confirm that the bus rolled, and Colson said she could recall no rolling. "All I remember was people screaming," she said.

Michael W. Long, 21, of Frederick, a motorist who said he witnessed part of the incident, said it appeared to him that the bus slid on its side for a time after striking the guardrail.

However, Tower, the state police spokesman, said last night that investigators believe the bus remained upright, and Colson said she could recall no rolling. "All I remember was people screaming," she said.

According to an account pieced together by state police, the bus went into a skid that turned it at a right angle to the roadway.

"The bus was skidding sideways down the bridge," Tower said. As a result, he added, it was the right side of the bus that struck the guardrail on the left side of the road.

The front of the bus was ripped open as if it were the top of a tin can. It remained attached only at the corner near the driver's seat.

In moments the bus rebounded, striking the right side of the bridge and then the left side again before coming to a halt about 100 or 150 feet from the point of first impact.

Tower said two persons were thrown from the front of the bus when it first crashed against the rail and others were flung from windows as it veered across the roadway.

O'Neal and Colson, neither of whom was seriously injured, said they remained in the bus.

"I braced myself against the seat in front of me," O'Neal said. When the bus finally halted, he said, he noticed only one other passenger still aboard. Otherwise, he said, "there wasn't nobody, nobody."

Colson said damage to the front of the bus forced her to jump to the pavement.

After seeing the injuries of her fellow passengers, she said, she was awed by her good fortune.

"God wasn't ready for me," she said after being released from Frederick Memorial Hospital. "The way I saw all those other people, and the only thing wrong with me is I'm skinned up on my knee and I strained my back."

"I just can't believe it," she told a reporter in Frederick.

Colson said she has been a regular on the race track trips, having made the journey each weekend for years.

"No, no, no," she said, when asked if she would make the bus trip again. "If I ever go again, I'll drive myself."

Four of those killed were pronounced dead at the scene. Brown, the driver, was taken to Suburban Hospital in Bethesda, where he died at 2:51 p.m.

By late yesterday, four of those injured had been released from Frederick Memorial Hospital after treatment.

Of the three who were critically injured, two were being treated last night at Frederick Memorial. The third was transferred by helicopter late in the afternoon from Frederick to the shock-trauma center at the University of Maryland hospital in Baltimore.

Four other injured persons remained hospitalized at Frederick Memorial and one at Washington County Hospital in Hagerstown, all of them in stable condition, authorities said.