MOST OF US think of a political campaign as a kind of debate: candidate X is for a tax cut, Y is against it, and the voters decide. But that is not how most campaigns are really fought. Shrewd candidates try to frame the issues in a way that is to their advantage. Thus different candidates and parties emphasize entirely different issues or themes.

That seems to be happening in the 1982 elections around the country. The theme Republicans are sounding in a great many races is summarized best by the tag line of their television ad: the friendly postman says, "For gosh sake's, let's give the guy a chance." "The guy" is, of course, President Reagan, and by "a chance" the Republicans mean that the voters should not elect so many Democrats that he will not be able to continue to get most of his programs through Congress.

The Democrats' theme is summed up in the phrases "fairness" and "mid-course correction." By emphasizing fairness, the Democrats suggest that the president's program has unduly helped the rich and hurt the poor and middle class. Mid-course correction means they will not get rid of all Mr. Reagan's policies, but they will trim excesses.

Both the Republican and Democratic themes seem to us moderate and slightly apologetic. The Republicans evidently feel that a wholehearted advocacy of Mr. Reagan's economic programs would lack credibility. As for the Democrats, we don't recall that Franklin D. Roosevelt and John F. Kennedy rallied their troops by calling for a "mid- course correction." Even in the fairness theme there is the implication that some of the Reagan budget and tax cuts were okay -- he just went a tad too far.

The bloodlessness of these themes does not mean that the election season will be entirely somnolent, however. Look at the Massachusetts Democratic primary for governor on Sept. 14. This is a kind of preview of the general election, since the incumbent Democrat, Edward King, takes Reagan-like positions (lower taxes, capital punishment, opposition to abortion), and his challenger, former governor Michael Dukakis, is much closer to most Northern Democrats. The race is marked by negativism and vitriol, with Mr. King getting the older, more blue-collar and more traditional support and Mr. Dukakis the younger, more suburban and more affluent voters.

The relatively bland national party themes do not really touch on noneconomic issues -- as though both parties were afraid to fracture their culturally disparate coalitions. The unusual virulence of the Massachusetts contest suggests that these cultural differences, rather than the economic issues, can spark real hatreds -- and distract us all from the issues that politics can actually resolve.