A Wheaton Rescue Squad truck skidded on wet pavement and smashed into a parked police cruiser as it approached a bad weekend accident in Rockville, setting off a chain reaction that left an emergency worker injured and at least three other vehicles damaged.

The 15-ton emergency vehicle was responding to a two-car accident late Friday at Veirs Mill Road and Claggett Road in which three people had been injured, one of them critically, police said.

"It crested the hill, and as it came down . . . the crash wagon started to fishtail," said Montgomery County police Sgt. Herman Lamberger. Then, he said, "it was sort of like a pinball machine."

The driver of the rescue vehicle, identified only as David Jones, was charged with negligent driving, police said. Jones was not injured.

Bill Walker, president of the Wheaton Rescue Squad, described Jones as a 15-year volunteer and "excellent" driver with long experience behind the wheel of the rescue truck, which is the largest emergency vehicle operated by the rescue service.

It was the second serious accident this year involving a Wheaton Rescue Squad vehicle. In May, a Burtonsville man was fatally injured when the car he was driving was struck broadside by a rescue squad vehicle that was headed south in the northbound lanes of New Hampshire Avenue in Silver Spring. The vehicle, which was using its emergency lights and siren, was heading for an accident a block away and was trying to get around stalled afternoon rush-hour traffic.

Authorities said yesterday there was no evidence that Friday's accident interfered with the response to the first set of victims, emphasizing that ample emergency equipment already was on the scene or arrived soon afterward.

The emergency worker who was injured, Kenneth Zseltvay, 36, of Rockville, was treated for a bruised hip at Shady Grove Adventist Hospital and released, authorities said.

Authorities identified the victims of the original accident as Beth A. Hess, 49, Phillis Shelton, 33, and Patricia Fuller, 44.

Hess and Shelton were treated at Shady Grove Adventist Hospital and released. Fuller was listed in critical condition yesterday in the intensive care unit at Suburban Hospital in Bethesda, where a spokeswoman said she was "progressing."

Rescue workers had been on the scene of that accident only a few minutes when the Wheaton Rescue Squad truck approached in the westbound lanes of Veirs Mill Road about 11:20 p.m., authorities said.

Police said the driver applied his brakes when he crested a hill and saw the other emergency vehicles parked on a shoulder near the median. Instead of stopping, however, the truck began to slide sideways, first striking the curb and two utility poles, then veering toward the median strip, the parked emergency vehicles and the two damaged cars with the occupants still inside.

Zseltvay, an emergency medical services officer for the county, was inside one of the cars attending to two of the victims when he heard the commotion. "I jumped out of the car when I heard people yelling," he said. At that moment, the rescue truck struck the police cruiser, which then struck another parked car, knocking it into Zseltvay.

That car then rolled across the eastbound lanes and plunged over an embankment and onto a service road. The rescue truck, meanwhile, ricocheted back across the westbound lanes and onto the service road on that side, where it hit two parked cars and a boat trailer and finally came to rest, police said.

Walker said the driver apparently did not expect to come upon the accident immediately after cresting the hill, and he suggested that the location of the accident could have been imprecisely stated over the radio.

Lamberger, however, defended police handling of the accident and said the rescue truck driver should have had ample room to slow down.

Lamberger said the cruiser was parked with its emergency lights flashing and that the distance from it to the top of the hill was nearly one-quarter of a mile.

Lamberger said the first accident occurred at 11:16 p.m. when a 1984 Toyota driven by Hess collided with a 1978 Dodge Omni driven by Fuller, who was accompanied by Shelton. He said he could not provide specifics on the accident but that it evidently occurred when one of the vehicles turned onto Veirs Mill from Claggett Road.

Walker said that Jones would be suspended pending a full investigation by a committee of emergency vehicle drivers.