EACH DAY it becomes more apparent that the government's handling of the investigation of Teamster President Jackie Presser qualifies as a first-class fiasco. People were understandably astonished when a 32-month grand jury inquiry into Mr. Presser's activities was suddenly abandoned. But the reason given for dropping a potential prosecution at this early stage is even more perplexing: Mr. Presser, we are told, has been working for some time as an informer for the FBI and the bureau had specifically authorized criminal conduct on his part. In addition, the defendant in a case long concluded will probably be released from prison because prosecutors are unwilling to reveal, at a retrial, the extent of Mr. Presser's involvement with the government.

At first there was suspicion that the investigation of the Teamster leader was being conveniently jettisoned because of his ties to the White House. His was the only major labor organization to endorse the president in 1980 and 1984. There is little talk of that any more, nor have there been charges that high officials in the Justice Department or the FBI were influential in or even knew of the relationship between the labor leader and the bureau. The Labor Department had also been conducting an investigation of the union, but by all accounts this department's agents favored prosecution and also had been kept in the dark.

Law enforcement officials must work with informants, co-conspirators and petty crooks because without their cooperation, and often their testimony, cases against racketeers, narcotics traffickers and corrupt officials would be almost impossible to make. Under strict guidelines adopted by the Justice Department and strengthened in the last administration, investigators may authorize an informano participate in criminal conduct -- but never violence -- in order to preserve credibility. Arrangements are made and informants supervised by a small group of people at the local level, and information about each case is kept tightly guarded in order to protect the informant's identity. It is at this level that the foul-up in the Presser investigation appears to have occurred.

Who made the deal with Jackie Presser in the first place? Why was a big fish like Mr. Presser given license to commit crimes just to catch a few little fish? Were there rivalries between Labor Department investigators and FBI agents that hindered the investigation? Why, when it was well known that a federal grand jury was working on this matter for almost three years, didn't the FBI tell the Justice Department about their arrangement? Law enforcement officials aren't answering these questions; they're conducting quiet internal investigations. But sooner or later the whole story will come out, whether by full disclosure or a series of leaks and accusations. This case will not stay closed.