Ten cars, parked on the quiet streets and driveways of a residential neighborhood near Rockville, were damaged by separate fires during a four-hour period early yesterday in what Montgomery County fire officials said was a possibly unprecedented incident of arson.

A 29-year-old Rockville man was arrested and charged with 10 counts of arson in connection with the blazes, which were reported between midnight and 4 a.m. within a mile-square section of Derwood, authorities said. They said they knew of no motive in the burnings.

County firefighters, who were called to combat the fires, most of which occurred on Camberford and Malabar streets, found it difficult to keep up with the outbreak, according to Capt. Ray Mulhall, a fire department spokesman.

"The fire department was on the street working on a fire and the next thing you knew, someone was telling us they saw flames up the street," Mulhall said. While firefighters worked to extinguish the blaze in one auto, he added, "there were at least two other fires going on at the same time."

The incident left in its wake surprise, consternation, the smell of burned rubber tires and varying degrees of damage to the 10 autos.

One of the vehicles, a 1981 Oldsmobile, parked in the 16800 block of Camberford Street, appeared gutted. Damage to another car, a Toyota Corolla parked nearby, was confined to charred upholstery.

For Elizabeth Brown, the owner of the Oldsmobile, the honking of her car's horn, apparently caused by the blaze, alerted her to it.

When she reached the window of her house, she said, she saw the car engulfed in flame, while neighbors clustered about in pajamas and robes.

"It was my baby and it's totaled," she said of the car. Also lost, she said, was a research paper completed recently in connection with her work as a sports psychologist and faculty member at the University of Maryland. It was under the driver's seat, she said. "I don't know why anyone would do anything like this," Brown said.

Jack Harris of 16829 Malabar St. learned of the incident while watching television about 12:30 a.m. "A couple of boys from the neighborhood pounded on our front door and said 'Hey, your car is on fire.' "

The car was a 1984 Nissan belonging to his daughter, Nancy Koschmann, who was visiting from New York. Harris said he tried to extinguish the blaze with a garden hose, but "it was too far gone."

Residents interviewed yesterday said that in at least some of the cases, papers from the cars' glove compartments were apparently used in starting the fires.

"We haven't had anything like this in such a short period of time," Mulhall, the fire department spokesman, said.

The suspect was identified as Robert George Johnson of 9611 Watts Branch Dr. Officials said he was being held in lieu of $10,000 bond in the county detention center. Details of the arrest were not immediately available.