Edmund Harnstrom, a 19-year resident of Prince George's County, on a recent Saturday moved to a Columbia condominium complex. Barely 36 hours later, he awoke to find an empty space where his 1986 Toyota Cressida, loaded with golf clubs, tools and other belongings, had been parked.

"I was shocked," Harnstrom said. "I've had many cars and I've never had a problem. I move here and the second night my car's stolen."

Especially shocking to Harnstrom was that his Toyota had been sitting next to a Corvette in the parking lot and several Mercedes-Benzes had also been nearby, yet none of those more expensive cars had been taken. "It was as though someone walked past all the other cars in the lot and said, 'That's the one,' " he said.

Howard County police officials say Harnstrom's experience is more than a case of bad luck. "There has been a big rise in auto thefts over the last year or so," said Sgt. Angus Park, a police spokesman. There were 340 auto thefts during the first six months of 1987, which represents a 51 percent increase over the same period in 1986, Park said.

But car thieves aren't in search of Rolls-Royces or Jaguars. Park said that Toyotas and Mazdas appear in crime reports more often than do other makes. Of the 129 cars stolen between Oct. 1 and Dec. 31 last year, 76 -- or almost 59 percent -- were Mazdas or Toyotas.

The main reason is that "their ignition system is easier to defeat" because of the design of the locking mechanism, Park explained.

The models popular with auto thieves here are the Mazda RX7 and 626, the Toyota Camry and Cressida, and the new Chevy Nova, which is built like a Toyota, Park said.

Police have noted that apartment complexes and town house developments close to major highways have been hardest hit. "It's not happening in single-family neighborhoods. There is greater variety in parking lots, there are no garages and thieves are less likely to be seen."

Most of the thieves are youngsters just looking for a joy ride, Park said. "The cars are stolen for fun, not profit," he said.

Often the cars are quickly dumped by the thieves, and the recovery rate is high, Park said. Park said only 25 of the 129 cars stolen during the last quarter of 1987 are still missing. "Usually we find them intact," Park said. "There might be some dents and the stereo might be missing, but that's the extent of it."

Howard police are trying to combat the problem by establishing stakeouts in certain areas and through community awareness programs that offer neighborhood groups tips about how to prevent car theft.

They also recommend that owners of high-risk vehicles invest in special locking devices for their cars, which cost about $25.

One Toyota dealer is making sure that his cars stay on the lot. John Farley, general sales manager at Toyota Village in Clarksville, said every Toyota without an alarm is blocked in by a car that has one. He reports that the crime wave hasn't hurt sales. "We can't get enough cars in," he said.

"Customers aren't overreacting {to the high rate of Toyota thefts}, but many customers purchase alarms," Farley said.

Not even an alarm helped Harnstrom. "It went off in the middle of the night; so what?" he said. Is Harnstrom racing out to buy a new Cressida? "I'd be scared to buy one as long as I live here."