POLICE NEED a warrant to search your home and probable cause to arrest you, but what about simply stopping your car and asking you to get out and answer a few questions? Should officers be allowed to do this at random, or should some objective test be met before such an intrusion is allowed? On Monday, the Supreme Court set a standard for justifying an investigative stop that is very low indeed. It ruled that an anonymous telephone tip, providing some information that turns out to be true, meets the "reasonable suspicion" test that justifies a stop.

Two years ago, the Montgomery, Ala., Police Department received an anonymous telephone call stating that a woman named Vanessa White would that afternoon be leaving apartment 235C at a certain address. She would be carrying an attache case containing cocaine, the informant said, would enter a brown station wagon with a broken taillight, and would drive to Dobey's Motel. Later, the police observed an unidentified woman leave the building in question, though not the specific apartment mentioned. She was not carrying anything. After entering the car described, she drove toward the motel but was stopped before reaching it. The police found marijuana in an attache case in the car and three milligrams of cocaine in her purse. The Supreme Court ruled that the stop and the subsequent search were permissible because a few of the clues provided by the unknown caller were verified.

In assessing Fourth Amendment rulings, it is important to remember that the courts only get these cases when incriminating evidence is found and criminal charges are brought. Thus the rules defining police powers are always written in situations where someone has been caught red-handed. The rules, though, apply to police conduct toward all citizens, not just those eventually charged with a crime. Thus does a standard set low enough to catch Vanessa White permit the harassment of those who have done absolutely nothing wrong.

As three dissenting justices pointed out, most neighbors can estimate when a person will leave his home each day, can describe his car and can predict that he will head toward his place of employment. An anonymous caller with a grudge can easily supply the police with these facts, and on this basis alone the target of such a caller can be stopped by the police and questioned. The dissenters are right that the decision makes a mockery of the Fourth Amendment.