DETROIT (AP) _ The car most popular with thieves last year wasn't a Porsche or a Jaguar: The most-stolen domestic car was a 1986 Chevrolet Camaro and the most-stolen import was a 1982 Toyota Corolla.

That's according to Certified Collateral Corp., a Chicago company that provides insurance companies across the nation with estimates of vehicles' market value.

Of the top 32 cars most often reported to insurance companies as stolen in 1987, all were General Motors Corp. models of various years starting with the 1986 Camaro, the company said. The top 10 also included the 1984, 1985 and 1982 Camaro.

Sam Barash, chief operating officer of Certified Collateral, said cars are usually stolen for parts, and said the parts on the various Camaro models are often interchangeable.

Camaro parts also can be used on the more expensive IROC version of the Camaro, ''a very hot car,'' he said.

Also in the top 10 were the 1981 and 1980 Oldsmobile Cutlass, 1986 Pontiac Firebird, 1984 Oldsmobile Cutlass Supreme, 1986 Chevrolet Monte Carlo and 1981 Buick Regal. Firebird and Pontiac TransAm parts also are interchangeable, as are parts between many GM models.

GM spokeswoman Jane Mott stressed that the company's cars were not easier to steal than others: ''Between 40 and 50 percent of the vehicles on the road are GM models. It's their prevalence on the road that makes them theft targets.''

The 1982 Toyota Corolla, the most-stolen import, ranked 33rd on the overall list, followed by the 1982 Toyota Celica. The third most-stolen import was the 1981 Corolla, followed by the 1985 Mazda RX7-GS sports car.

Barash said the imports at the top of the list were older than their domestic counterparts because the foreign cars are holding their resale value longer, creating a market for parts.

He also noted that although the Camaro, Firebird, Mazda RX7 and Toyota Celica are not as high-volume as other cars on the list, they are sporty cars often owned by younger people who drive them hard and wreck them often.

''The driver of the (Chevrolet) Celebrity, or (Plymouth) Reliant K is probably far less often in the kind of accident where they need to get parts,'' Barash said.

''The driver of that RX7 is driving a hot car, thinks he's got himself a Porsche for the price of a Hershey bar. He drives it like a hot car and cracks it up a lot more.''

The cars that seem most likely to head the list, exotic Porsche, Jaguar, BMW or Mercedes models, didn't appear among the 100 cars that account for the largest numbers of thefts.

In part it's because comparatively few of them are sold, Barash said. But in addition, he said, parts from one of Porsche's three models cannot be used on the other two. Jaguar, BMW and Mercedes parts also cannot be switched from one model to another.

Certified Collateral compiled the rankings from 99,865 vehicle market value estimates it provided to insurance companies during 1987 for vehicles reported stolen. In all, it provided insurance companies with 700,000 market value estimates for claims on damaged or stolen cars last year.

In 1986, the most-stolen domestic model was the 1984 Camaro while the 1983 Corolla topped the import list.