Minor political events in this spring of 1986 give the first glimpse of the most serious threats to the two political parties in the upcoming presidential campaign of 1987-88. The minor events are the recent prominence of Jesse Jackson as a major spokesman for the Democratic left and the success of evangelicals associated with Pat Robertson, first in the Republican congressional primary in Indiana and last week in filing Republican precinct delegates in Michigan.

Both of these television-era ministers threaten to lead their parties in directions most other political leaders do not want to go. Almost no one expects Jackson or Robertson to be nominated for president. But even in losing they still can lead their parties some distance in the direction they want.

Of the two, the lesser if more familiar force is Jackson. His issue positions -- support of massive government spending, sympathy for Cuba and the PLO -- are widely unpopular, and much of his appeal comes from assumptions contrary to fact -- that he was the first black presidential candidate, that conditions for blacks in the South were just as bad as 20 years ago. Though he comes from the civil rights movement, he is less than alert to threats against civil liberties and public civility, reluctant to criticize the ravings of Louis Farrakhan and happy to embrace Fidel Castro.

Yet he is back again. He strikes a genuine enough chord with black voters to win 18 percent in the latest Post poll, and he could easily be one of the top two finishers in the regional primary that southern white politicians so gleefully promoted. He won't be nominated. But as in 1984, he will help define what the Democratic party is, and the nominee will be faced with the no-win choice of propitiating him or antagonizing his constituency.

Robertson represents a larger and even more enthusiastic constituency. In Indiana, a Robertson-backed candidate beat the strongest Republican party machine in the nation in a Republican district; in Michigan Robertson's Freedom Council claims plausibly to have filed 4,000-plus of the 9,000-plus precinct delegates. The potential is there for masses of new evangelical voters to overwhelm the thin ranks of registered Republicans -- ranks especially thin in the South.

Republicans with economic grievances have mostly been satisfied: inflation and taxes are down in the Reagan years, GNP up. But Republicans and potential Republicans whose grievances are cultural are still desperate to stop what they consider trends toward immorality and away from traditional values. In Robertson they have a candidate who shares their passion and anger and who also has the elite credentials -- son of a senator, Yale Law, sophisticated command of issues -- that most of their spokesmen conspicuously lack.

Robertson and Jackson, if they run, will be vivid candidates in a field in which even front-runners George Bush and Gary Hart are hazy figures to most voters. Both Robertson and Jackson are practiced TV performers, as aware as Ronald Reagan is of how their voices and body movements project over the tube. They are also adept at symbolism: Jackson has been courting protesting farmers, and Robertson's "700 Club" co-host Ben Kinchlow is black.

Jackson and Robertson are authentic representatives of important demographic constituencies and cultural attitudes. But does their appeal have much to do with government? Jackson is a symbol of black pride at a time when black advances seem to depend more on individual effort and discipline than on government action. Robertson is a champion of traditional belief in absolute values at a time when government increasingly lacks the capacity to regulate individual conduct. In different ways both are seeking cultural rather than political and governmental goals.

Moral example does count for something, and cultural symbolism can win some elections. But cultural politics is dangerous in a diverse country. Campaigns are not just theater where attitudes can be struck and ideas advanced: there are consequences. It is dangerous to make appeals that widen rather than narrow the divides between cultural groups. It is dangerous also to use government to impose the moral values of a temporary majority-plus-one on the rest of us: that is one of the things Robertson complains, with some justice, liberals have done.

Working politicians of both parties are concentrating on such workaday issues as tax reform. Jackson and, more seriously, Robertson threaten to lead their culturally defined constituencies toward a politics of enthusiasm. Their successes this spring -- especially Robertson's success in beating a strong Republican machine and running strong in a state that was 2-to-1 for Bush over Reagan in 1980 -- raise the chances that a politics of enthusiasm will overwhelm the politics of workaday government in one or both of our parties.