Fred Wertheimer, the new president of Common Cause, has an ingenious idea that could solve one of the more vexing problems that has popped up recently in our politics. It is the question of how to deal with "independent expenditure groups" that come into a state or district, not to help elect a particular candidate but to defeat someone else.

The most publicized of these groups, which claimed to have scalped several liberal Democratic senators in 1980, is Terry Dolan's National Conservative Political Action Committee.

NCPAC moved in early in such states as Idaho, South Dakota and Indiana--months ahead of the formal selection of a Republican challenger --and began advertising campaigns aimed at the records of the Democratic incumbents.

Encouraged by the victories in those races in 1980, Dolan's group has started in on an expanded program of "targeting" for 1982.

Other groups are seeking to imitate the technique, and liberals have organized at least three groups of their own to fight fire with fire.

The clear prospect is that unless some way is found to break the cycle, the airwaves and newspaper pages are going be filled with a rising volume of "negative ads" blasting away at Senator Jones or Representative Smith.

What is wrong with that? you ask. Assuredly, Sen. Jones and Rep. Smith miss no opportunity to tell their constituents how lucky they are to have such great men speaking for them in Congress. And the Supreme Court has held rightly that when Congress legislated limits on campaign spending, it could not constitutionally abridge the right of individuals or groups, operating independently of the candidates, to say through advertising what they thought of the merits or demerits of the aspirants.

Acknowledging all that, there are still two or three things about the independent expenditures groups that are troublesome. They are not really accountable to anyone but themselves and--as NCPAC's example shows-- they are not exactly scrupulous about the evidence they use in their roundhouse swings at their targets.

If politics were as closely refereed as, say, hockey, Dolan would have spent a lot of time in the penalty box.

Second, the din of negative advertising does tend to denigrate and drown out the healthy debate between candidates and parties that ought to be the heart of any campaign. And an avowedly independent negative campaign can tilt the odds in a contest by softening up the incumbent or forcing him to spend from his own funds, not against his opponent but against this outside group.

Wertheimer's suggestion is ingeniously simple: provide a right of free reply for the target of the independent expenditure campaign. For every negative ad that is run attacking him, give the person under the gun equal time and space, without charge, to respond.

What I like about the idea is that it effectively discourages the negative campaigns without impairing what is, I think, an important constitutional right to organize such a campaign. Any body would still have the right to get up on the soapbox and holler.

But he would know that the fellow he was hollering about would be right up there next to deliver his rebuttal.

Obviously, if every dollar an independent expenditure group spent attacking Sen. Jones created an equal entitlement for Jones to reply, free of charge, the utility of such a negative campaign would be severely diminished. Contributors would be harder to find--and so would media outlets for the ads.

There would still be room for independent campaign expenditures. A group that wanted to go off on its own and publicize its views on policy issues or its support for a particular candidate, without consulting anyone else, would still have the freedom to do so. But if it chose to attack someone, it would do so with the knowledge that its target would gain an automatic right of reply.

My guess is that the effect of such a rule would be to return responsibility and control of the election campaigns to the parties and the candidates, which is where they belong. It strikes me as an idea that is worth Congress considering when it takes up the question of federal election law amendments later this year.