SUPPOSE YOU are on a bus to Baltimore that pulls into the Silver Spring station to pick up more passengers. In addition to a couple of travelers, three policemen get on the bus. They are wearing badges and uniforms, and one of them is carrying a black zipper pouch that clearly contains a gun. The policemen go up and down the aisle asking passengers to produce tickets and identification. Then they announce that they'd like to search 10 or 20 pieces of luggage to look for drugs. Wouldn't you assume they had some kind of warrant or probable cause to believe there were narcotics aboard? In Florida you wouldn't be able to assume any such thing. This might just be a police fishing expedition.

It is the procedure Florida police call "working the buses." They regularly climb aboard vehicles that have left Miami and go through this routine -- without probable cause and with no reason to suspect any individual passenger of being a courier. Terrance Bostick was on a Miami-Atlanta trip when the police came aboard in Fort Lauderdale and found cocaine in his bag. The police swear that they asked his permission before they searched his belongings, but he claims he did not give consent. The trial court believed the police, but the Florida Supreme Court reversed the conviction, even assuming that the search was voluntary. The court ruled, rightly we think, that the circumstances of the stop -- police blocking the aisle, the suspect unable to walk away and one policeman with his hand inside the gun bag -- amounted to an illegal seizure of the defendant, which also tainted the search.

Yesterday the Supreme Court agreed to hear an appeal in this case. That announcement is ominous because it means that at least four justices (not counting Justice Souter, who did not participate) believe the state court may not be right.

For more than two decades the Supreme Court has been broadening the search and seizure power of the police, allowing brief investigatory stops without probable cause, for example. But so far, these have been allowed only in situations where a suspect is on an open street, in a public place such as an airport or in his own car, where he has the option of turning around and avoiding a checkpoint. The Florida practice is different in important respects because a passenger, hemmed in by police, unable to avoid confrontation, is much more likely to feel intimidated and to believe that he cannot refuse consent to a search. The whole procedure smacks of coercion and a creeping government encroachment on the Fourth Amendment. The Florida court was right, and its ruling should be sustained.