A plush $164,173 Rolls-Royce Corniche, stolen Monday from a Bethesda car dealership, was found near Philadelphia International Airport yesterday. It was a pleasant surprise to authorities who feared the car would be shipped abroad.

Police and Michael Jackson, general manager of the dealership where the car was stolen, said the theft may have been the work of professional thieves who planned to sell the car overseas. Although Philadelphia police staked out the car for 10 hours, no suspects were arrested.

But the unidentified person who discovered the car has earned a $10,000 reward.

"There are a lot of places in the world where people would buy a car like that," said Gerald Cassidy of the insurance firm of Early, Cassidy and Schilling Inc. "Even a stripped down Chevy is worth two or three times its value in places like South America."

In the first six months of this year, 5,829 cars were reported stolen in the major Washington area jurisdictions, or more than 32 a day, according to police statistics. Nationally, 1,141,077 cars were stolen in 1980, and only 55 percent were "recovered," statistics from the National Auto Theft Bureau show. But the term recovered is misleading, since only the engine and transmission have to be intact to be considered part of that category.

Local and federal authorities said many of the thefts are simply for "joy rides." Others, Montgomery County police said, are stolen and stripped for parts within an hour of the theft at "chopshops," or illegal warehouses where stolen cars are stripped.

"They are stolen and shipped abroad from ports in Newark, Baltimore, Philadelphia and Wilmington," said U.S. Customs officer Joe Tedeschi of Newark who once discovered there more than 100 stolen Oldsmobile Regency, Chevrolet Caprice and Buick Electra autombiles bound for oil-rich Kuwait in the Middle East.

"The export of stolen vehicles is a big problem area because there are no real operating controls at work to stop it," said Tim Kett, public relations director for NATB. He said that between 10,000 and 20,000 stolen vehicles are driven to Mexico each year, quoting figures released during a congressional subcommittee hearing on stolen autos in June.

Trying to seize the stolen autos is compounded by a lack of manpower and the enormous quantities of goods shipped abroad from eastern ports each year, Tom Cleary of NATB said.

Dennis Murphy, a spokesman for the U.S. Customs Service in New York, said that an another ploy is to have the cars cut in half, buried inside containers beneath other goods and shipped abroad. CAPTION: Picture, The $164,173 Rolls-Royce stolen here earned Philadelphia finder $10,000. AP