THERE IS NOT much to be gained by speculating about how the latest chapter in the Abscam affair will end. The prosecutors, past and present, are apparently divided among themselves as to how close the investigators came, in some of the bribery cases, to the line that divides a legal snare from an illegal trap. The defense attorneys, of course, think the line was crossed. The judges, as they always do, will have the last word.

But there is something to be gained from looking -- in the abstract -- at the tactics used by the government in this remarkable investigation. According to the Department of Justice, those tactics pretty well followed the guidelines set out last week by Attorney General Civiletti as official policy for future undercover investigations.

If that is so, the Justice Department and the FBI tried hard to keep the Bascam investigation on target.

The guidelines provide, for example, that before a government agent invites an individual to engage in illegal conduct -- as the Abscam agents did when they offered bribes to members of Congress -- the "corrupt nature" of the conduct must be "reasonably clear" to the potential victim. The inducement offered -- $50,000 in most of the Abscam cases -- must also be in line with the character of the illegal transaction.

Those are useful and wise guidelines, meant to eliminate the possibility that a victim does not understand the illegality of what he is asked to do and is not tempted by sums of money out of line with reality.

But after that, the guidelines move into a treacherous area. They permit the director of the FBI to authorize his agents to offer bribes to individuals who are not suspected of having previously engaged in similar illegal activities.

This is pushing the law and the legitimate role of law enforcement agencies too far. It is acceptable, legally and as public policy, for FBI agents to offer bribes to members of Congress when there is reason to believe they have sold or are willing to sell their services. But it is bad public policy and perhaps legally wrong for those agents to test the honesty of any public official (or anyone else) unless that threshold of prior questionable conduct has been crossed. No law enforcement agency should be in the business of running around town offering bribes, willy-nilly, in hopes someone will accept something. After all, the agent who offers a bribe is committing what would be an illegal act but for his official position.

This issue has yet to come to the surface in the Abscam trials. It may or may not come up in the future, depending in some part upon the prior activities of the men who were indicted. But whether or not it arises in these cases, the present attorney general or the next one should review these new guidelines with an eye to striking out this particular grant of authority to the FBI. While it is unlikely that the present director would abuse his power, the history of the bureau is reason enough not to have such a provision lying around waiting for someone to invoke it as a routine test for determining honesty.