A Sticker to Deter the Sticky-Fingered : Auto theft: Window decal allows police to stop car between 1 and 5 a.m. without reasonable grounds.

Someone you never met is driving your car at 2 a.m. You are at home asleep. Police wonder if it’s been stolen. Unless there are reasonable grounds to stop the vehicle, there’s nothing they can do.

But under a program launched last weekend by the Los Angeles Police Department’s West L.A. Area, officers will be able to stop the car if it has a small yellow decal in the back window that says: “Member, Operation C.A.T.--Combat Auto Theft.”

To get the numbered decal, car owners must to sign a form stating that they normally do not drive between 1 a.m. and 5 a.m. and that police are permitted to stop the car during those hours.

In effect, that waives the car owner’s constitutional right against unreasonable search and seizure until the decal is removed, a concept some legal experts find novel and somewhat questionable.

But police in New York, who came up with the idea six years ago, are convinced that the program works as a deterrent.

In a typical year, one of every 15 cars in New York City will be stolen, said Detective Tom Clavin of the New York Police Department’s Crime Prevention Division. For cars registered under the C.A.T. program, the theft rate is one in 574.

Officers normally need reasonable grounds for stopping a car--a traffic violation, outdated plates or some other suggestion that all is not as it should be.

“If it’s got a C.A.T. sticker you don’t have to worry about it,” Clavin said. “You don’t get questioned in court, ‘Why did you pull him over?’ He had the C.A.T. sticker in the window and that’s that.”

A prosperous area with many upscale cars, West Los Angeles was an obvious choice for the LAPD to test the C.A.T. program.

About 350 cases of auto theft are reported every month in the department’s West L.A. Area, which is defined by La Cienega Boulevard on the east, Mulholland Drive on the north and the Santa Monica Freeway on the south.

Among the prime neighborhoods for auto theft, officers said, are the blocks east and south of the UCLA campus and the apartment areas of Brentwood.

“A lot of those places don’t have secured garages,” said Detective Sgt. Mike Brambles, head of the LAPD’s West L.A. auto theft detail. “It’s a shopping center for the crooks up there.”

“There are more serious problems like murder, rape and robbery, but the problems that touch the most people in West L.A. are car-related,” added Sgt. Bob Brounsten, a community relations officer in the West L.A. Station.

The thieves are rarely out for a simple joy ride, Brambles said. Instead, the cars are generally stripped for parts or sent as far away as Central America for resale. Other stolen cars are kept in the area and re-registered with fake numbers after the vehicle identification number is filed off the engine block.

Brounsten credited the Auto Club of Southern California for introducing the program to the region and said several smaller police departments have been using it for months.

“We think it will help in combatting auto theft and reduce auto insurance premiums,” said Bob Dabinett, manager of the Auto Club’s Century City office. “If we can do that, we’ll accomplish something, because this is the auto theft capital of the world.”

Although Clavin said the sticker program has been tested in court and found effective, UCLA law professor Peter Arenella said he wondered about the effect on the Bill of Rights protection against unlawful search and seizure.

“The possibility of forever surrendering one’s Fourth Amendment rights raises novel questions,” he said.

What if someone else is driving the car with the owner’s permission? Can the owner undermine that person’s right against unreasonable search by posting a decal in the rear window?

“Even a car thief has, unless he’s an escapee from prison, a liberty that’s protected by the Fourth Amendment,” Arenella said.

“You’re going to have some real questions if the owner can waive the rights of a friend who has the OK to drive the car,” said Prof. Charles Whitebread of the USC Law School. “I think we’re going to have some fun with it.”

But Arenella added: “The fact that the owner affirms that the car is not used between 1 a.m. and 5 a.m. . . . makes the police argument of suspicion somewhat stronger. (Is) it strong enough? The courts will have to decide.”

Be that as it may, the point is to discourage car theft, Calvin said. “From the point of view of car theft, it’s cut and dried,” he said.

The West Los Angeles police station is at 1663 Butler Ave. Decals can be obtained there on weekdays from 8:30 a.m. and 5 p.m.