Denouncing the character and competence of one's campaign opponent has gotten a bum rap lately. Negative advertising by a candidate can frequently make a positive contribution in a political campaign. Consider three cases from this year's Senate races:

* As the old line goes, Rep. Robin Beard wanted to run "very badly" for the Senate from Tennessee. And in 1982, he did just that, becoming the victim of serious voter backlash and outrage at his campaign commercial that pictured his opponent, Democratic incumbent Jim Sasser, as buddy to and benefactor of Fidel Castro.

* California's Democratic Gov. Jerry Brown broadcast a commercial that argued, because Brown's GOP Senate opponent, Pete Wilson, opposed the nuclear freeze, that Wilson was "soft" on a nuclear holocaust.

* Sen. Harrison Schmitt of New Mexico was the only Republican incumbent to lose this year. He used a commercial accusing his opponent, state attorney general Jeff Bingaman, of freeing a convicted felon when, in fact, the U.S. Deartment of Justice had requested the release of the prisoner into its custody so that he could testify at a trial for the murder of a federal judge.

Beard, Brown and Schmitt all paid for their televised smears; all three will return to private life in January. The voters quite properly held these three grown men answerable for their advertised distortions.

Negative advertising by candidates is not the real problem. The real problem is the so-called independent committee, which spends its own money, and frequently as much as the candidates do, in trashing one of the candidates. The National Conservative Political Action Commitee is only the best-known. The election saw the emergence of allegedly liberal clones of NCPAC which, instead of condemning Edward Kennedy in their direct-mail appeals for contributions, went after Sen. Jesse Helms of North Carolina. Helms' Senate term does not expire until 1985, but he is almost as much of a bogyman to the political left as Kennedy is to the country club and capital gains set.

Negative advertising by independent committees in 1982 sometimes proved to be less of a problem for the targeted candidate than for his opponent. In 1981, NCPAC proposed targeting 20 senators who sought reelection this year. Nineteen of them won. In some races, being the target of NCPAC enabled an embattled incumbent to run against "outsiders," thereby ignoring his challenger's criticisms and appealing effectively to the home-state voters' sense of fair play.

These independent committees -- unlike the candidates with the examples like Beard and Brown before them -- have no limits imposed upon them. The committees do not have to win 55 percent of the vote. The committees rely solely on the solvency of the political paranoids whose checks they cash and whose fears they flatter. The problem of negative politics in our campaigns is not a candidate problem. The problem is quite simply those independent committees that distort and frequently diminish the campaign dialogue and that are run by people who want to control campaigns but who do not have the guts to run themselves. The answer is simple: leave the campaigns to the candidates; they are accountable, and they live by limits.