IF YOU THOUGHT this city had serious drug problems before, consider the ramifications of what is happening now: U.S. Attorney Joseph diGenova has announced that 300 to 400 drug cases will be dismissed in response to allegations that some narcotics officers in the 4th Police District may have stolen drugs and money during raids. The heart of a city's law-enforcement effort against drugs has been severely damaged -- and the anxieties of drug-plagued neighborhoods heightened dramatically. The only satisfaction is in the ranks of a booming narcotics trade that has now been given new leases to push and deal. Was this necessary?

With no firm knowledge of how broad this FBI investigation of police will turn out to be, it is difficult to assess Mr. diGenova's decision, which the prosecutor said was agreed to by Police Chief Maurice Turner. Certainly the scope at this point is broad -- involving an entire police squad: all pending cases that are based on evidence gathered by the 4th District vice squad. Word that the entire squad has been replaced, at least temporarily, also does little to dash suspicions that the investigation is covering much ground.

Even though most officers of the squad have not been implicated and no charges have been filed yet, the difficulty is that defense lawyers could challenge the cases by claiming that the other officers may have known about the alleged skimming. Mr. diGenova has noted, however, that charges in the hundreds of drug cases are being dismissed "without prejudice," meaning that the government could bring them again later.

Speed is critical -- for the sake of every police officer, for the reputation of the department and for the salvaging of every case possible. In the meantime, the effects of all this are devastating to residents whose lives and homes are threatened daily by the drug trade on their streets. If even one officer did what is alleged, must it taint years of enforcement work by others? Here, as in other investigations led by Mr. diGenova, the residents as well as their government officials should not be left hanging indefinitely.