"The function of law enforcement is the prevention of crime and the apprehension of criminals. Manifestly, the function does not include the manufacturing of crime."

Those two sentences, made by Chief Justice Earl Warren back in 1958, express the two rival interpretations that have been built up around the ABSCAM investigation. Unfortunately, it turns out to be very hard to determine whether the present case involves crimes committed by corrupt public officials or crimes fostered by diligent officers of the Federal Bureau of Investigation. So the first requirement is a guide to the investigations -- a way to probe the probers.

The basic details of the case are plain enough. In the course of an ongoing investigation into the sales of stolen securities and art objects, the FBI came into contact with what appeared to be several rings of political fixes. The bureau invented a phony sheik and a phony company and put out the word that the sheik and his company would make various kinds of payments to public officials for various kinds of services.

According to reports leaked to the press, several local officials were caught red-handed accepting bribes to grease the way for a gambling casino in Atlantic City and a hotel in Philadelphia. A senator and seven members of the House were also said to be implicated.

The published evidence suggests that the inquiry is well founded. Naturally, the Justice Department wants to finish the investigation, present the evidence and go to trial. And one view of the case is simply that a brilliant FBI effort caught some politicans with their dukes in the tambourine.

But the other view emphasizes that something more than just a neutral investigation or wrongdoing is at stake. The tactic of baiting traps to catch crooks -- the so-called "sting" technique -- has been in practice for several years. But normally the targets are habitual criminals -- especially loan sharks and drug dealers. It is a far different matter to use the technique on public officials -- especially members of Congress who have some responsibility over the law-enforcement agency.

In this case, however, the law-enforcement agency has a distinct self-interest. The FBI is still reeling from revelations of poor, and in some cases corrupt, performance under J. Edgar Hoover. It has a public reputation to reestablish.

A leader in the drive to refurbish the bureau's image is Associate Director Neil Welch, who is currently in charge of the New York field office. Welch, who at all times resisted the Hoover approach, originally made a name for himself in the Philadelphia area, where he directed the investigations that yielded indictments of Reps. Joshua Eilberg and Daniel Flood of Pennsylvania. He has also been the moving spirit in the ABSCAM investigation. If only because of the assets mobilized for the case -- in both dollars and the time of many agents -- the bureau could not afford to have ABSCAM fail.

Moreover, the Justice Department in the Carter administration was not likely to scrutinize the investigation very closely. In Justice, as in so many other departments, including Interior and State, the ideological do-gooders have become the arbiters of policy. Attorney General Benjamin Civiletti, like Judge Griffin Bell before him, has been unwilling to shut off prosecutions that should have never been brought -- for example, the cases against the Philadelphia Police Department, against Hamilton Jordan of the White House staff, against IBM and against the Reynolds tobacco heir, Smith Bagley.

Finally, there is one bit of evidence from the ABSCAM case itself. Sen. Larry Pressler of South Dakota was approached by FBI agents purporting to represent the phony company and was exonerated. As he tells the story of the approach, he didn't ask for illicit action; he was invited to participate. If a crime had occurred, it would have been manufactured.

In these conditions, ordinary citizens face a genuine dilemma in trying to ascertan whether crimes were committed or manufactured. Two tests assert themselves, at least as regards the federal officials.

First, there is a matter of how the senator and various representatives became targets for the ABSCAM approach. If the leads followed from an ongoing investigation, then there is a strong case. But if they were fed into the hopper by the bureau itself out of some generalized suspicion or by reason of proximity to other people, then the case ought to be regarded with a very fishy eye.

Then there is an institutional test. Certain public bodies, particularly in local government, really are corrupt. The Democratic organization in Philadelphia seems to be a case in point. There is reason to suspect the city council in that town. But the tough standard that might be applied to an institution with a reputation for corruption ought not to be applied to the odd senator or representative who has no such institutional connections.

Until all the evidence is in, sensible people will keep an open mind as to whether crimes were committed or manufactured. The one sure thing is that the leaks were deplorable, and the Justice Department, if it wants to be taken seriously, has a responsibility to do something about them.