For those who discovered (or, more likely, inherited) their political parties in an earlier age, the shocker this fall is the news that youth is flocking to Republicanism.

Republicanism? Yes, there are findings to show it. In the latest Harris Survey, Ronald Reagan leads Walter Mondale by 13 points among 18-and 19- year-olds. Other opinion findings show a tidal shift of party identification. The Democrats have lost about 15 percentage points in 10 years. Republican spoilsmen and strategists are licking their chops, dreaming of a "realigning election," in which these trends will be sealed into something like permanence.

Excuse me, but the business looks fragile and uncertain from my vantage point. True, younger voters do tend these days to slip ancestral political moorings almost lightheardedly, an indication that history has either lost its grip or hasn't visited them yet.

A sense of the past, if it does nothing else, helps objectify loyalties in politics. You feel that your views are more than merely selfish, that they're prompted by some larger general interest as well.

In my own southern boyhood, this sense remained powerful. One might become a Republican; many of my contemporaries have done so. But not, I suspect, without guilt, a sense of betrayal and uprooting.

The deterrent forces included, in approximate order of importance, two powerful memories: there was President Herbert Hoover, a grim old man who lived in the Waldorf Towers and who was believed to have tolerated, if not caused, the miseries of the Depression. And much before that, there had been the Grant Republicans, who had given us Reconstruction.

That this past was in some respects imaginary made no essential difference; what mattered was the memory.

In talking now about politics with people in their twenties, I find that the past, if known, is not felt as a keen presence -- and in any case not considered to have a bearing on present political loyalties. Gone are the ominous memories that kept the Republican temptation safely distant 30 years ago. The new generation, as my old Air Force drill sergeant used to say, are like chickens, "waking up in a new world every day."

Moreover, I sense a greater economic wariness. No one starting out 25 or 30 years ago worried about finding a job at his level of professional competence or craft. Most of us expected to surpass, as a matter of course, the Depression and war-straitened economic circumstances in which we had grown up; and most, in fact, did so.

Now, the experts tell us, the middle class is in danger of shrinking, or sinking; and the job market is unstable and unpredictable. Writing recently on the lure of Reaganomics for Yuppies, Brett Fromson of Fortune Magazine confirms this element in the new appeal of Republicanism.

To be sure, he gives it a twist that older heads may find novel -- that the Republicans stand for opportunity, the Democrats for stagflation. The Democrats, writes Fromson, "remind me of American automakers. The Republicans are the Japanese."

Finally, there is the crowning astonishment: Democrats apparently are losing the battle of personality. The youngsters apparently view the Republican-Democratic choice primarily in terms of the contrast between Jimmy Carter and Ronald Reagan, the two presidents they directly remember, and rather at the expense of Carter.

This is the peril of historical shallowness, but never mind. It is the puritan Carter against the hedonist Reagan; the uptight Carter against the laid-back Reagan, and so on: preacher versus smoothie; shortages versus expanding horizons; goom versus optimism.

In the pairings we remember, it was very different. Warmth, wit and optimism always seemed, somehow, to favor the Democrat. Herbert Hoover, of whom it had been cruelly said that if you put a rose in his hand it would wilt, was no match for the jaunty Franklin Roosevelt. Nor was Thomas E. Dewey, pedantic "little man on the wedding cake," a match for Harry Truman. And even Dwight Eisenhower, the famous general, seemed a bit slow and solemn beside the elegant, witty Adlai Stevenson. In the contest of qualities that warm the young heart, there was no Democratic disadvantage.

And now what? Reagan, the old trouper, is as dangerously charming as Carter was not. In their history-less state, the young float among loyalties with no haunting sense of ancestors stirring unhappily in their graves -- so far.

But my suspicion is that historical experience finally does more "realigning" than campaigns, and has a way of paying unexpected calls. History may already have finished the political education of the Yuppies. But I wouldn't bet on it.