The small but lethal civil disorder in Miami last week, which left two dead and a score of persons injured, started off in depressingly familiar fashion. Two police officers entered a video game arcade frequented by young blacks and became embroiled in a confrontation with a 21-year-old man named Nevell Johnson, who worked as a messenger for the Dade County government. It ended with one of the officers shooting Johnson fatally in the head.

Whether the shot was fired out of perversity or in self-defense, or whether it was accidental, will be investigated by no fewer than five separate inquiries. For many Miami blacks, however, the verdict was immediate: the policeman was guilty of a cold- blooded killing. And having small faith that any punishment would be meted out by the system, Johnson's contemporaries went out and vented their anger in the streets.

As far as the rioters were concerned, it didn't matter much what actually happened in the shooting. Racial disturbances are touched off not so much by the precipitating incidents themselves as by how the incidents are perceived to symbolize a general trend in police behavior. Thus rioters condemn the police as much for their ordinary conduct as for what they did in a specific instance.

The sparks that ignited the 1960s riots in Watts, Newark and Detroit were all preceded by a number of well-publicized examples of what blacks regarded as police injustice that did not lead to riots. Similarly, the incident that ultimately led to the Miami riot of 1980, the killing of a black insurance agent, Arthur McDuffie, had been only the most recent of several police transgressions. Others included the molestation of a black girl by a state trooper and the killing of a young black man in neighboring Hialeah. Had the McDuffie killing been seen as the exception rather than the rule of police conduct, it seems doubtful that blacks would have rioted.

It is axiomatic, of course, that poverty and hopelessness are preconditions of urban disorders. The well-off do not riot, even if sorely provoked. But since we seem incapable of quickly reducing black unemployment or improving ghetto housing, it is the police, for all practical purposes, who hold the key to preventing riots. So, other than advising them against employing racist psychopaths, what should we tell them to do?

One thing would be to recognize the failure of superficial solutions left over from the 1960s, such as hiring more community relations officers and providing in-service courses aimed at reducing racial prejudice. Community relations officers, because they tend to remain isolated and powerless within their departments, get as little respect on the street as they do from their colleagues. And ethnic history courses, it has been discovered, often reinforce the racial stereotypes they're meant to dissolve.

It would be more fruitful to recognize that many of the provocative incidents occur when the police lose their heads, and to begin teaching officers skills they can use to increase their defenses against panic. One of these would be a thorough grounding in the martial arts, which would provide them some alternative to shooting people to death or beating them up. "Hitting a person over the head with a flashlight," one Miami police official told us, "is not the best way of bringing him under control."

Another idea, and one supported by many black groups, is to make them more familiar with the people by putting the neighborhood patrolman back to walking a beat. In Miami, as in many cities, the method of patrol is to send a pair of police officers out riding aimlessly around their sector, car windows rolled up, air conditioner blasting away, much as if they were cruising in a mobile isolation booth. The only time they leave their car is to answer a call or to eat, and even then the Miami police prefer to go over to Hialeah rather than eat in the black areas of Liberty City or Overtown. "It's a lot easier," said one Miami police captain, "to shoot people you don't know."

Assigning officers to foot patrol is hardly a new idea, and officials are ready with quick criticisms. Policemen don't lik beat work because it is less pleasant than riding around all day chatting with one's partner. The higher-ups argue that the beat system reduces mobility and hence is more expensive. But in the few places where it has been seriously tried, the system's advantages seem to outweigh the objections. One of these has been the industrial city of Birmingham, England. There, an experiment called "community policing"--which amounts to putting bobbies out on the sidewalk and giving them firm instruction as to how they're to treat citizens--practically eliminated assaults on policemen and greatly reduced complaints by West Indians of police brutality. And when the riots hit the kingdom in 1981, Birmingham experienced far less trouble than anywhere else.

At the least, a conscientious beat officer in the Overtown section of Miami almost certainly would have dropped in on its major video arcade as part of his rounds. He might also have gotten to know Nevell Johnson, and he might have conceivably found some way to overcome whatever the problem was that night other than by shooting him to death.