The quadrennial moan over the quality of presidential candidates is louder than usual this year. It is accompanied, as it always is, with much puzzlement over why "the system" prefers ordinary men to rare and remarkable ones, as though the land were studded with great men who have been shoved aside by the public appetite for the mediocre.

Actually, greatness is no rarer than it ever was. If great men and women were numerous they wouldn't be unusual enough to be great. We've probably only had seven great presidents. George Washington in the 18th century; Jefferson, Jackson and Lincoln in the 19th; the Roosevelts and Wilson in our own. There were a few others like James Madison who were great men but lousy presidents.

By now we ought to be used to having an ordinary kind of guy in the White House. There are some pluses to that also. The British historian Lord Action remarked that "Great men are almost always bad men."

Greatness is not goodness, as a quick study of the great figures of history from the Emperor Darius to Adolf Hitler shows. Them's that are hollering loudest for a candidate of higher stature may be the ones to cry the longest if they get their wish.

Any president who would be able to do what people are clamoring for Jimmy Carter to do would be a menace. Imagine the danger of a man who could unify the country, give us a sense of national purpose, stop inflation, lick unemployment, free the hostages and make the Russians grovel.

To listen to a lot of Americans talk, you have to conclude they don't want a president; they want a fuehrer or a Moses. The same people who complain about excessive government regulation are calling out for a president who will order them hither and thither, tell them what to do and how to think. For all who demand leadership of a president, may I suggest Fidel Castro. He even styles himself "the maximum leader."

Oh, not that kind of leader, the leaderless will tell you. But that's the only kind of leader there is. Naturally, we'll have to make certain cosmetic changes in Fidel before we let him move into the White House. The beard must go. This is a capitalist country where a lot of people have their money invested in Gillette. He will also have to cut down his speeches; three-hour prime-time harangues will not wash on American television. Castro brings an additional benefit with his leadership qualities -- he'll solve the Cuban refugee problem in Florida. The moment he arrives in Washington, all those folks will go home.

Great leaders are more apt to create problems than solve them. The great Roosevelt was never able to beat the Great Depression; what he was able to do was to give the population goose pimples while they listened to a master orator use the radio as no subsequent American politician has been able to use broadcast media. It's interesting, though, that the most popular 20th-century president with both Democrats and Republicans is the decidedly ungreat Harry Truman.

There is little to say for him as a president and less as a unifying, strong national leader. He left office when the country was suffering from inflation and divided over a long, costly, no-win war in Asia, but we cherish this stubborn, incompetent little man's memory, perhaps for his feisty, eccentric, impractical independence, scarcely the characteristics we say we yearn for in the masterful, leaderful president of our political dreams.

If we do get a great leader, we'll have to work on our fellowship. The 10,001 special interest groups that crisscross our society, veto each other and frustrate presidents will have to get used to taking orders. And since we belong to those groups ourselves, we'll have to get used to taking orders, too, but hallelujah, and by gum, we'll have a leader, a great man in the White House.

Any system that must await the coming of individual greatness to work is inherently defective. That's one of the reasons monarchy has passed out of fashion. It's wonderful when you have an Edward III on the throne, but then comes a drooling, hemophiliac crown prince. Ours is a system that makes a great nation with mediocre, not-so-great men. So bring on Ronald Reagan and Jimmy Carter for the main bout and be thankful they're no better than they are.