One minute, the employes of a Radio Shack store in Fairfax City were looking out the window at a two-car collision on Rte. 50. The next minute, one of the cars had crashed through the front window and was sitting in the midst of the store's computers.

"Charles yelled: 'Look out! She's coming through the store!' " manager Dick Maher said one of his salesmen warned the eight or so shoppers. "As she hit, she smacked me in the butt," Maher said.

Miraculously, a fire department spokesman said, no one was injured yesterday when Helen Hemley's car sped in reverse across the eastbound lane of the rain-slick highway, entered the Kamp Washington Shopping Center's parking lot and smashed through the store at 11046 Lee Hwy.

Sgt. J.R. Robertson of the Fairfax City Fire and Rescue Service said the impact of the collision on Rte. 50 apparently caused Hemley's car to go into reverse gear and locked the gas pedal to the floor, sending the car into the store. There it came to a stop next to the "Electronic Toyland Now Open" sign.

Hemley, of 11701 Foxvale Ct. in Oakton, was trying to cross Rte. 50 for a left turn, Robertson said, when her burgundy Chevrolet station wagon was struck by another car. The name of the driver of the car that struck Hemley's was not available yesterday, according to Fairfax officials.

Hemley was charged by Fairfax City police with failure to yield the right of way, Robertson said. No charges were filed in the Radio Shack crash, which caused an estimated $10,000 in damage to the structure of the store and left a gaping hole in the window. There was no estimate available for the damage to the store's merchandise.

"We looked up to see what the deal was," said Charles Chrosniak, the salesman. "There are accidents out there all the time."

"All of a sudden . . . she flew in," said Chrosniak. "She was doing 35 mph . She just sat there. We tried to get her to turn the thing off."

Maher said smoke filled the store after the tires of Hemley's car skidded while entering the store. Frightened customers ran out the rear of the store, he said.

"We had computers all in the window," said Maher, surveying the damaged computers, stereos and television sets sitting among the broken glass and Christmas decorations. "I just turned the heat off. No sense heating the outside."

"I'm glad we went to the library before we came," said customer Linda Lieberman of Burke, as she walked by the front of the store, which will be closed for an undetermined period while repairs are made.