A Supreme Court ruling this week allows police to use drug-sniffing dogs during routine vehicle stops even if officers have no particular reason to suspect illegal activity.

Stemming from a 1998 Illinois case, the 6-2 opinion states dogs can only sniff the exterior of a car if a motorist is pulled over for a traffic infraction.

The case involves Roy Caballes, who was stopped by Illinois police for driving 6 mph over the speed limit. Although Caballes lawfully produced his driver's license, troopers brought over a drug dog after noticing air freshener in the car and noting Caballes appeared nervous.

The dog indicated drugs were in the trunk, and police searched it even though Caballes refused to give permission.

They found $250,000 worth of marijuana, and Caballes was convicted of drug trafficking. The verdict was thrown out by the Illinois Supreme Court, which ruled the search was improper because police had no particular reason to suspect Caballes had drugs.

In his opinion, Justice John Paul Stevens reversed the state court ruling, saying the intrusion into Caballes' privacy was too minimal to invoke constitutional protection.

"A dog sniff conducted during a concededly lawful traffic stop that reveals no information other than the location of a substance that no individual has any right to possess does not violate the Fourth Amendment," Stevens wrote.

In a dissent, Justice Ruth Bader Ginsburg bemoaned what she called the broadening of police search powers, saying the use of drug dogs will make routine traffic stops longer and more adversarial. She was joined in her dissent by Justice David H. Souter.

Chief Justice William H. Rehnquist, who is ailing with thyroid cancer, did not participate in consideration of the case.

Closer to home, Monday's ruling has little effect in Douglas County. Lt. Steve Orr, head of patrol for the county's sheriff's department, said deputies ask for the motorist's permission or obtain a search warrant before using a canine to search vehicles. The process is required by the Nevada courts, he said.

"I think the restrictions we have in Nevada lessen the potential abuse by authorities," Orr said. "I don't anticipate a change with the procedure used by this agency."

Usually there are indications of illegal contraband in the vehicle. The occupant's behavior, a distinguishable odor in the car, or visible drug paraphernalia can persuade authorities to search the vehicles.

"It's not just picking a car down the road and saying 'I'm going to search it for drugs.'" Orr said.

In El Dorado County, consent or a search warrant is not needed to tour a certified drug dog around a vehicle, according to Hans Uthe, assistant district attorney in El Dorado County.

Uthe hasn't heard of an instance where authorities use a dog without suspicion in South Shore.

"Every time I've seen one used, we've already had a very fair suspicion," he said. "I have never seen the dogs used randomly."

Even though law enforcement has an assured safeguard in traffic stops leading to the discovery of drugs or other contraband, Uthe said the decision ultimately rests with the respective agencies.

"It may result in a change of officers' behavior in the field or it may not, because there's the law, then there's policy," he said.

But privacy rights advocates said the ruling would lead to far more traffic stops as a way to find drugs. They also warned that the decision could open the door to more expansive searches, from sniffs inside the vehicle to checks of cars parked along sidewalks and pedestrians on the street.

Before Monday's ruling, the Supreme Court had authorized drug dogs primarily to sniff luggage at airports.

Most of those questioned had slim knowledge of the ruling or just read about the findings in newspaper or Web site reports.

South Lake Tahoe Defense Attorney Jordan Morgenstern believes police dogs have a useful purpose, to an extent.

"On one hand it could result in the loss of privacy. On the other hand it could be a useful tool in the right circumstances," he said. "As a criminal defense attorney I have to be somewhat leery of the officer's use of drug-sniffing dogs where there might be no probable cause present."

Paul Palant, another South Shore defense attorney, said the ruling erodes privacy rights.

"It makes our job a lot more difficult and a lot more lucrative," he said.

El Dorado County sheriff's Deputy Damian Frisby, an upcoming canine handler for the department, said he will use his discretion when to use the dog.

"I'm very cautious on stuff like that," he said.

- The Associated Press contributed to this report