In a PBS interview the other night, Gary Hart rather testily justified his reentry into the presidential race with the claim that he is as well qualified for the great office as anyone in ''200 years.''

Armed with that high estimate of his capacities, Hart plans to take his campaign over the grubby heads of the political-punditorial establishment and directly to The People. Should this populist strategy work, the result would not be altogether unwholesome. For Hart, however overinflated, is certainly right in claiming that the landscape is overcrowded with political brokers.

But before Hart gets the chance to sit where his alleged peers Washington and Lincoln sat, he will have to lay aside distracting ghosts of a lesser presidential presence, Richard M. Nixon.

Hart's little prevarications about his age and name changes, his early political influences, his bent for furtiveness, remind one uncomfortably of earlier debates about Nixon's character, about the succession of old and new Nixons. To this day no one -- perhaps least of all Nixon himself -- could say which was the real one. Hart, too, seems a bit mercurial.

This, incidentally, was a strong impression well before his early years or his ''womanizing'' surfaced as issues. Hart is of my own generation. Yet he comes across as quite a bit younger, physically and politically. The physical clock runs differently for everyone, but what about the political clock?

Hart missed or pretends he missed major political influences common to his generation and mine -- influences such as the Eisenhower-Stevenson elections and their meaning for the American future as we saw it; McCarthyism and red-baiting and the hangover from the Hiss case; the Korean War and Hungary and J. Robert Oppenheimer and the debate over the hydrogen bomb. Did he tune these things out? Or did they wash over him without effect, while leaving the rest of us indelibly stamped?

Only Hart knows the answer; but here's one provisional theory. Today, the 1950s have assumed for younger people the romantic haze that for Hart's generation and mine hung over the ''roaring'' 1920s. Of course, that decade roared only for those who learned about it secondhand from F. Scott Fitzgerald novels and Frederick Lewis Allen's ''Only Yesterday''; it's the myth that matters.

The 1950s aren't a chic era for today's aspiring ''generational'' politician to take bearings from. They were too dull, too conventional, too disengaged (by hearsay, anyway). Your model modern politician must pretend that the political world was abruptly created in the election of 1960 and the advent of Kennedy and Camelot -- that before that year zero, all was without form and void in presidential politics.

In keeping with that myth, Hart presses his claims as the candidate of ''ideas'' -- so much so that he says it was the failure of his Democratic peers to advance them that drew him back into the race, for America needs them.

The claim, again, is more than faintly Nixonian in tenor -- off-key, if not phony. One is hard-pressed to think of any significant political idea with which Hart is identified -- in the sense that Bill Bradley is identified with tax reform or Sam Nunn with a conceptual mastery of strategic military affairs.

Even if there were a patented Hart ''idea'' or two (a real one, as distinguished from slogans about ''reinvestment'' and ''enlightened engagement''), they would not be very useful in the primary caucus races. A politician of his seasoning ought to know that. Presidential campaigns, and presidencies, too, are rarely exercises in ideas. Indeed, successful presidents (FDR is the outstanding example) are remembered for their ability to slide from expedient to expedient without dragging heavy doctrinal anchors.

It is puzzling that Hart harps on his originality as an idea man. Maybe he is still licking the cut Walter Mondale inflicted four years ago with the question ''Where's the beef?'' from the hamburger ad.

As one who condemned as ''totalitarian journalism'' the inquisition that pushed Hart out of the race, I agree with him that even candidates are entitled to a zone of privacy. But Hart now is attempting to blur pertinent questions about character and background into nosy prying into his private life. That won't wash.

Voters resist, as they should, the suggestion that the presidency is to be entrusted to a stranger. Hart remains a stranger -- in part, one suspects, because he is in some mysterious way a stranger to himself.