A Silver Spring man was critically injured yesterday at a Rockville antique car show when an 80-year-old man lost control of his vintage Rolls-Royce and backed over the other man, who was sitting near an antique Buick he was exhibiting.

The 1958 Rolls-Royce struck Floyd L. Bubel, 73, in the chest. He was conscious after the accident, police said, and was taken by helicopter to Suburban Hospital in Bethesda, where he was in critical condition last night.

The accident brought to a standstill the 39th annual city-sponsored antique car show, which attracted about 10,000 visitors yesterday.

Police said Joseph W. Gaskill, 80, of Bowie, was trying to back his Rolls-Royce into his assigned display position across from Bubel's late-1950s Buick.

"Mr. Gaskill failed to maintain control of his vehicle, which drifted forward and struck [Bubel, who was] sitting on a lawn chair," said Rockville police Lt. Charles Holzberger.

Gaskill told police that when he realized the car was rolling forward, he pumped his brakes without effect. Police examined the Rolls-Royce's brakes and found them in good working order, Holzberger said. Gaskill has not been charged with a traffic violation.

"Technically, it's not considered a traffic accident," Holzberger said. "It did not occur on a public roadway. Therefore, there probably will not be any traffic charges."

Burt Hall, Rockville's director of recreation and parks, said this was the first injury in the history of the annual one-day car show, which is held at Glenview Mansion in Rockville Civic Center Park.

"It's an event that all the car owners look forward to every year, and it's unfortunate this show was blemished by this accident," he said.

This year, 470 cars were on exhibit.