THINGS GOT A BIT dirty in the last days of campaigning in Fairfax this month, and the head of the country's Fair Campiagn Practices Commission thinks the state legislature should do something about it. Her suggestion for action, while catchy, is a bad one: Leslie Byrne thinks the Gerneral Assembly should forbid distribution of campaign literature in the seven days before an election.

There has been cause for concern in Fairfax. In 1975, when the county supervisors created the commission, both major parties agreed to abide by a code of ethics. But some candidates have refused to sign a commitment that they, as individuals, will campaign according to the code. Even if they violate the code outright, the commission has no enforcement powers anyway. It can only cite a candidate.

That happened at the eleventh hour of this year's battle between Republican John M. Thoburn and Senate Majority Leader Adelard L. Brault. On the Sunday morning before the election, Catholic voters in the district reported receiving flyers stating that Mr. Brault had opposed a convention to consider a constitutional amendment backed by anti-abortion forces; it also said that he had supported a "pro-abortion" congressman. Mr. Brault, a Catholic, notes that he has consistently supported anti-abortion positions. Other flyers stated that he had voted for an increase in the states sales tax on food -- though he had voted against such proposals.

Mr. Brault brought charges against his opponent, and the commission cited Mr. Thoburn on two counts of unethical campaigning. Mr. Brault then posted Election Day signs noting the citations and portraying his opponent as a "dirty trickster." Mr. Brault also won the election. Since then, both sides have complained about these events: Mr. Thoburn's supporters charging that the actions contributed to his loss, and Mr. Brault voicing dismay at the number of last-minute charges by candidates and at the fact that the media rarely publicize such charges.

There is no simple remedy. If the media were to broadcast and print such charges in the final hours, candidates on all sides would be even more tempted to smear opponents, who would have no time left to issue rebuttals. In turn, the commission system does not -- and cannot -- guarantee clean, uplifting campaigns by everyone seeking office. The only judges with real authority over the success or failure of any campaign -- and who should view last-minute allegations with caution and skepticism -- are the voters.