FLOATING AROUND in various quarters of Capitol Hill is one of the more dreadful ideas in circulation these days -- one that should be dispatched before it does real damage. The idea is that a federal law is needed to cut down on the amount of "negative advertising" in political campaigns. The proposals being made are non-solutions to a non-problem. There is no reliable evidence of an upsurge in anti-opponent campaigning in 1986 or 1984, just a general impression based on some fairly vicious ads. Actually, if you compare American politics of the middle 1980s with American politics in the past or with contemporary politics in other countries, the pitch made in this country at this time seems downright benign. Nor is it obvious why campaigning against one's opponent is always such a bad idea. A far worse idea, surely, is to call in the cops -- i.e., the federal government -- to influence the character of political argument.

One proposal, put forward by Sen. Daniel Evans (R-Wash.), would force candidates to appear throughout broadcast ads in order to qualify for the low rates that the law currently guarantees political advertisers. Another measure, currently part of the Senate campaign finance reform package, would require candidates who want to stay eligible for federal matching funds to stay on the air for 50 percent of any ad and deliver personally any attack on an opponent. Such proposals cause problems at the margins -- just what is an attack, anyway? -- and would give an advantage to candidates who are telegenic. They put a straitjacket on political debate. Once you start down this road, where do you stop?

The place to stop is the beginning. The best way to regulate the content of political advertising is to let the voters do it: candidates have the strongest of incentives to avoid any campaign tactic that antagonizes the voters. Robust political debate is best obtained when candidates are free to make their case the way they want.

We understand how politicians may be tempted to support proposals to elevate the tone of political discourse -- especially if it means keeping their opponents from saying nasty things about them. The temptation should be resisted. Let politicians work up codes or rules among themselves for campaigns, if they want to. Let voters and commentators and other kibitzers raise hell, if they please, and see if they can force politicians who offend them by their campaign style to clean up their act. Let the federal government keep out of it. We favor legislation that would cut the amounts the candidates could raise and spend -- but not legislation that tells them how to spend it.