Before the 1988 election is over, a lot of sanctimonious humbug will be written, pro and con, about Jesse Jackson's candidacy. I think, to put my cards on the table, that it offers a disastrous temptation for the Democrats.

I say that as an admirer, within limits. Jackson won my esteem when, as a student leader at North Carolina A&T College in Greensboro, he led the open-accommodations marches in the summer of 1963. The demonstrations were a great success, resulting in the desegregation of most public facilities in Greensboro well before the passage of the Civil Rights Act. It was an impressive accomplishment, not foreordained even in a civilized city.

Jesse Jackson is still a man of ideas -- good ideas. His recipe of personal responsibility and self-esteem is the right stuff, and not just for young blacks. He is a powerful speaker, capable of stirring the most jaded audience.

Why then, having said all this, do I view Jackson's candidacy as a potential disaster? In such matters, one has only intuition and history as guides; and the possibility of subtle racial prejudice can't be ruled out.

But political qualifications are always in the eye of the beholder. And in the eye of this beholder, it is clear that a white clone of Jesse Jackson would not be taken seriously as a presidential candidate -- by anyone. Voters are weary of political preachers, and politicians do not usually start at the top, as Jackson seeks to do. To collaborate in the pretense that Jackson is taken seriously as a presidential candidate except for reasons of liberal condescension is itself a form of subtle racism.

Jackson, moreover, has recently focused his considerable brainpower and energy on one of the more quixotic projects of recent years: the ''rainbow coalition,'' which history foredooms. American presidential politics is coalition politics, all right, but not that kind. Coalitions built exclusively of the deprived whose ''time has come'' are no more appealing to most voters than some self-proclaimed cabal of the rich and privileged.

And there is something else about Jackson's core constituency. Next to Gary Hart's courtship of the yuppie vote in 1984, the most astonishing feature of the Democratic race was the discovery that many of Jackson's young black followers knew nothing about the civil-rights movement, and utterly lacked a sense of the significance of such familiar figures as Andrew Young and Coretta Scott King. What could they know of other important things, one wondered, if they knew so little of the central fact of recent American history?

Jesse Jackson's most dubious habit, however, is to chase after, and identify with, whatever emergency or human cause happens to be hot. He even turned up in Geneva last year to admonish Mikhail Gorbachev about the refuseniks. It was such showboating that led The Post to say, with unusual waspishness, that Jackson is in danger of becoming the greatest ambulance-chaser in American politics.

Jesse Jackson is not an impediment to Democratic prospects in 1988 because he is black, but because he is Jackson. No Democrat will be elected -- at least, none ever has been -- without southern electoral votes. A ticket headed by Jackson would not attract them. This may be discreditable to the American voter, but it is a fact. There has been only one presidential election in modern American history -- 1964 -- whose circumstances permitted a Democratic candidate to adopt, with impunity, nearly the whole agenda of civil-rights activists. And that was because people like Bull Connor and the San Francisco Republicans (who nominated Barry Goldwater) cooperated so beautifully.

The urge to test the tolerances of American voters has been a consuming itch within the Democratic Party for nearly 20 years. The Democrats may scratch it once again by nominating Jesse Jackson. If they do, it will make the Republicans' day.