ONLY WEEKS AFTER all hell broke loose in Miami, there is grim news again -- scattered shooting, a stabbing, melees and other acts of violence. This time the spark was an arrest in the deeply troubled and still-scarred Liberty City section of town, where the tinder for such social explosion remains dangerously dry. So why again?

The first wild rioting in May captured the attention of the rest of the country -- momentarily. But the sorry state of police-community relations in Miami did not and could not disappear in a brief shower of public attention and federal sympathy. For that matter, many of the local authorities themselves still do not seem to have a sense of what has been happening around them, at least not if they believe a police spokesman there who commented that "we're not referring to this as any sort of racial problem."

When an overwhelmingly white police force uses an undercover "robbery suppression team" to swoop in and arrest black youths in connection with holdups of motorists -- and when a crowd gathers and shots are fired and disorders continue for hours -- like it or not, a city has racial problems. When that city has a long history of serious allegations involving violations of civil rights and brutality, it has widespread perceptions of injustice that feed racial tensions. When a city has an unemployment rate among blacks that is double what it is among whites, and when waves of Cuban immigrants threaten to take what few jobs may be left, there is bound to be frustration and rage.

What else has happened in Miami since May? President Carter made some vague promises of federal aid and drew boos and bottles as he motored quickly out of Liberty City. State lawmakers from the area rejected a proposed sales-tax increase to help rebuild the riot-torn blocks. The last contingent of national guardsmen went home. A ban on gun sales was lifted. And federal investigators continued to look around. Is it any wonder that the tension still abounds? The response to Miami has to be something more than a set of post-riot studies and then back to business as usual. It is going to take the concentrated efforts of federal, state and local leaders to deal with the alienation that plagues Liberty City.