THOSE WHO HAVE suffered at the hands of roughneck police officers anywhere cannot help noticing that all of a sudden U.S. Attorney General Benjamin R. Civiletti has led a team of some three dozen federal prosecutors, U.S. marshals and FBI agents to Miami to investigate "all serious allegations involving violations of civil rights and brutality" over at least the last five years. After the riot, there is a deluge of federal help -- and better late than never -- but how did police-community relations reach such a sorry state before these authorities moved in to take an official look?

There is no question that the federal presence in this explosive situation is enormously important and welcome now. Regardless of what specific legal actions do or do not result from these investigations, the fact is that longstanding grievances and allegations will be aired -- and listened to, for once. This official review of abuses and indifference should lead to some constructive changes. But quite aside from questions of federal government aid to cities and their poor and jobless minorities, what besides a riot does it take for Washington to sense and react to a string of alleged civil rights violations?

In describing his mission in Miami, Mr. Civiletti referred to "a great perception of injustice, which has brought a sense of frustration and rage." He meant this not as an apology for the horrible crimes of those who rioted, but as an accurate assessment of what a large segment of Dade County residents have known, discussed and feared for years. And when local officials don't do enough or simply aren't able to erase such a perception over time, police officers may sense the permissiveness; a wartime mentality can develop and brutality can be rationalized.

Officials of the Justice Department's relatively small and underused Community Relations Service, which monitors racial and other tensions around the country, say they have been aware of such problems in Miami "for the last 10 years" but never had money to open an office there. They also say they've been warning local officials in Miami about police-community relations all along. "They're listening now," said one. "It's usually before a riot that they don't listen." They're not the only ones listening now, either: Mr. Civiletti says the Community Relations Service will get that office after all.