The cries of disillusionment about the scope of John F. Kennedy's White House tapes remind us again what a fine line separates the respect for presidents from the tendency to make demigods of them.

In a republican system, political leadership cannot be entirely disinfected of a certain ersatz royalism. And the courtiers attracted to the life-sized men who occupy the White House for a season are prone to project idealized virtues upon them.

Thus Arthur Schlesinger Jr., who as a historian should be wary of the foibles of politicians, was quick--too quick--to declare in July 1973 that Kennedy couldn't have done what Nixon did: secretly tape intimate conversations. It was "absolutely inconceivable . . . not the sort of thing Kennedy would have done."

It was, alas, all too conceivable. Why did Schlesinger think otherwise? He is probably a victim of the illusion that his more partisan writings have helped perpetuate: that some politicians are especially immune to the temptations of power and human vanity.

Historians of Schlesinger's brilliance really ought to be forearmed against confusing personal and partisan loyalty with ultimate political principles. They should be warning us to remember Lord Acton's warnings against the corrupting character of power, and James Madison's about the un-angelic character of human nature--not joining the mindless rush to heroize presidents they happen to agree with or esteem.

Modern electronic devices are treacherous servants to presidents seeking to strike the right balance between appearance and reality. To the mischief of television we must now add the false "candor" of the tape recorder, which is sure to magnify the impression that petty confusion is inseparable from great decisions.

Why, then, do presidents run the risk? Because they are vain about their ultimate standing in history. At least that seems to be the standard excuse.

For instance, in his recent White House memoir, John Ehrlichman advances the speculation that "Nixon had particularly wanted the White House taping system . . . to demonstrate that the foreign policy initiatives of his presidency were in fact his own, not (Henry Kissinger's)."

The theory is consistent with what has been elsewhere reported about Nixon's envy of Kissinger. But Ehrlichman, even so, is a suspect witness. He still maintains, although an April 25 tape proves otherwise, that he learned of the Nixon taping system only when Alexander Butterfield disclosed its existence to the Ervin committee in July 1973.

When the extent of the Kennedy tapes became known last week, one eminence of the Kennedy years said that he would have been more careful if he had known that "history was listening in."

That, at least, is one misplaced worry. "History" was not listening in unless you confuse history with an unedited and unevaluated transcript. Random and fragmentary discussion in a president's office or in the Cabinet Room bears about the same relationship to history proper that an electrocardiogram bears to biography. It is a piece or two of a complex mosaic.

It was an instructive coincidence, on that score, that the same week yielded both the Kennedy tapes story and the harrowing transcript of the last confusing minutes of Air Florida's Flight 90. The cockpit talk seemed at times frivolous and carefree, although in that respect it is probably quite misleading about the competence of the two pilots.

But just as the Nixon tapes seemed to indicate, in part, that presidents routinely say unmentionable things about foreign currencies, the Flight 90 transcript may persuade the public that pilots routinely jest about ice on the wings.

It won't be surprising if the Kennedy tapes, once transcribed, reinforce the cynical impression that there is a lot of flying blind in the Oval Office. Some there is, no doubt. But as a general rule of judgment, that impression would be as false as the impression that some presidents are natural eavesdroppers while others are immune to that temptation.