WASHINGTON — The Supreme Court yesterday expanded police power to conduct searches, ruling that an officer who stops a motorist for a routine traffic violation can use a drug-sniffing dog to detect narcotics in the vehicle, even if the officer had no reason to suspect the car would contain drugs.

The decision, in an Illinois case, gives law enforcement the authority to use drug-detecting dogs in the course of any minor traffic stop.

"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," Justice John Paul Stevens wrote in a 6-2 decision.

Dissenting Justices David Souter and Ruth Bader Ginsburg said the decision allowed police to turn any routine traffic stop into a drug investigation and "clears the way" for dog-accompanied drug sweeps of cars stopped at traffic lights and parked along sidewalks and in garages.

"Under today's decision, every traffic stop could become an occasion to call in the dogs, to the distress and embarrassment of the law-abiding population," Ginsburg wrote in her dissent, which Souter joined.

Chief Justice William Rehnquist, generally a staunch supporter of law enforcement, had just begun treatment for thyroid cancer when the case was argued in November and did not participate in the decision. He has said he would not take part in any of the November cases unless the court was deadlocked 4-4.

The decision reversed a ruling by the Illinois Supreme Court, which had said police violated Roy Caballes' constitutional rights when they searched his car after he was stopped for going 71 mph on Interstate Highway 80 in LaSalle County, where the speed limit is 65. While an officer was writing him a warning, another walked around his car with a dog.

The dog signaled the presence of drugs in the car, so officers searched the trunk, found 282 pounds of marijuana and arrested Caballes. He was convicted for trafficking in marijuana, sentenced to 12 years in prison and fined $256,000.

Ralph Meczyk, Caballes' lawyer, criticized the Supreme Court decision, saying it goes well beyond what the court has previously allowed, giving police "unbridled authority" to conduct searches of vehicles. He said that "erodes all citizens' constitutional rights."

The Illinois court had ruled such searches illegal, curtailing police ability to use drug-sniffing dogs. The officers should not have used the dog, the state court said, because police did not suspect Caballes was carrying drugs.

In his opinion reversing the Illinois court, Stevens stressed that the Supreme Court was resolving only the narrow question of whether police had to have some suspicion of drug activity before they could use drug-sniffing dogs after a traffic stop.

Stevens concluded the answer was no. A drug sniff did not raise legitimate privacy concerns, the court said, because the narcotics-detecting dog exposed only illegal drugs, not other items that would otherwise be hidden from view. It therefore does not violate the Fourth Amendment, he wrote.

But Meczyk and the dissenting justices said Stevens failed to appreciate how often the drug-sniffing dogs are wrong. One study showed dogs could falsely alert authorities to the presence of drugs more than half of the time, Souter noted.

In other cases yesterday

Brain-damaged woman: The justices refused to get involved in the case of Terri Schiavo, clearing the way for the husband of the severely brain-damaged Florida woman to have her feeding tube unhooked by a state court order. The justices dismissed without comment Florida Gov. Jeb Bush's claim that he had the power and responsibility to keep Schiavo alive after a state judge authorized removal of the tube. Schiavo, 41, has been in a vegetative state for nearly 15 years.

License plates: The court declined to consider whether states may offer license plates with anti-abortion messages, leaving lower courts divided over whether the programs in a dozen states unconstitutionally restrict dissenting views.

Sentences: The justices asked federal courts to reconsider sentences for hundreds of defendants who contend they were wrongly punished under a sentencing system the court declared unconstitutional earlier this month.

Information on other cases was provided by the Los Angeles Times

and The Associated Press.