THERE'S A CERTAIN tendency, when you hear that a member of Congress has been indicted, to wonder whether someone has finally gotten the goods on a cheating politician. But there has been a considerably more skeptical response in the case of Rep. Bobbi Fiedler (R-Calif.). She was indicted by a grand jury in Los Angeles last Thursday on charges of agreeing to help Ed Davis, one of her opponents in the Republican Senate primary, pay off $100,000 in campaign debts in return for his leaving the race.

Mrs. Fiedler is accused of violating a law that prohibits using money to induce someone else not to be a candidate for public office. She insists that in the transaction in question there was to be no quid pro quo. There is no allegation that the money that would have been applied to pay off the Davis debt would have consisted of anything but legal and declared campaign contributions.

But what sort of law is this? The California statute, passed in 1893, was apparently copied from an 1883 English law, and the leading scholar on the subject, UCLA Prof. Daniel Lowenstein, says that so far as he can determine it has not been used since. The law has the look of a standard anti-bribery statute. But bribery law prohibits the making of public decisions for private gain. The decision to run or not to run for office is not a public decision: no one has a duty to run for office.

It is difficult to find a persuasive consideration of public policy supporting this law. On the contrary, helping pay off a former opponent's campaign debts is a common practice. It strengthens party unity and ensures serious contests in general elections. Supporting a former opponent in this way is not one of those gray-area practices of which it is said, in exoneration of the latest instance, that "everyone does it." It is a legitimate party-building device.

The California law is one of those old criminal statutes that clutter the books in many states. A responsible prosecutor ought to be very chary of using this sort of law as the basis of an indictment. The case burst in the middle of a fiercely contested 10-candidate race for the Republican Senate nomination. Almost every candidate has some plausible claim on the nomination, and none has a significant lead with the voters. District Attorney Ira Reiner, a Democrat, has yet to explain satisfactorily why he used an obsolete statute in a way that interferes with the other party's choice of a nominee in a major election.