A Maryland appeals court has ruled that police may no longer randomly stop cars for "routine checks," but must instead have a "reasonable suspicion" to believe the occupants have violated a specific law.

Random stops violate a motorist's constitutional guarantees against unreasonable searches and seizures the Maryland Court of Special Appeals ruled Wednesday.

Although state and local authorities offered different assessments on how frequently such stops are made, they acknowledged yesterday that officers randomly stop citizens' cars for driver's license and registration checks in certain circumstances.

Montgomery County police officers "do quite often look for suspicious vehicles and do make stops based on suspicion," according to Capt. Thomas McDonald, head of the department's patrol division.

McDonald recalled an instance two years ago when there had been a murder and attempted murder in an area of Silver Spring, and police "were flooding the area, stopping anybody and everybody to find a starting point on an extremely serious crime."

A Prince George's County police spokesman said county officers do not generally make random stops but might, for instance, stop suspicious vehicles late at night in an area where there had been a rash of crimes.

A state police spokesman said the ruling would have little effect on his department. Nevertheless, the department's legal adviser yesterday directed that no officer "shall 'randomly' stop any vehicle unless there are reasonable grounds."

Prior rulings by the Court of Special Appeals seemed to permit random traffic stops, according to Assistant Attorney General Stephen Caplis, who argued the case for the state. But the court Wednesday, in anopinion written by Chief Judge Richard Gilbert, overruled prior decisions that had sanctioned such stops.

Caplis also said Maryland police departments recently had recognized that other state high courts were prohibiting such stops and had moved to curtail them.

Yesterday's ruling came in the appeal of a Baltimore criminal case in which a car was followed, then stopped by Baltimore City police because it appeared to be a "suspicious vehicle," although the driver did not violate any traffic laws. Three guns were subsequently found in the car and two passengers were later found guilty of firearms violations. The appeals court threw out the convictions, finding that the stop had been illegal and the recovery of the guns was an unconstitutional seizure.