Back when Milton Berle was "Mr. Television," he used to greet applause by holding up one hand to indicate "stop" while the other beckoned for more. From Berle, the routine was funny. From Mario Cuomo, who is essentially doing the same thing, the routine is both vexing and undignified.

The conventional wisdom of the moment is that Cuomo is serious about not being a presidential candidate. He has said so himself -- most recently in an interview with Tom Brokaw on NBC. He will do no campaigning and enter no primaries. If, however, the Democratic Party turns to him he will -- because it's his duty -- accept a draft.

That sounds pretty firm -- the one hand held up to say "stop." Cuomo's other hand, though, is his schedule, statements and demeanor. He is more or less on the stump. In addition to speaking in New York, he has accepted invitations elsewhere -- all the time setting a high standard for both thought and eloquence. He is treated like a candidate because he acts like one and, indeed, there are vague signals he might become one. New York is rife with rumors to that effect -- including one that Cuomo's family no longer opposes a presidential race.

At the moment, Cuomo is the Democratic Party's leading kibitzer. Refusing to sit down at the game himself, he nevertheless has an opinion on how everyone else is playing. Lately, he reportedly has become dissatisfied with the play of Michael Dukakis, from whom he expects broader statements on the economy. Such reports do not materialize out of nowhere. Cuomo is a master manipulator of the press. Dukakis was put on notice: shape up or Cuomo might start favoring someone else, maybe Sen. Paul Simon.

There are good reasons for the continuing fascination with Cuomo -- and no one knows them better than the New York governor himself. None of the Democratic presidential candidates has yet caught on. A gathering of Democrats is a somber affair, replete with mutterings about "leanings" and peopled by procrastinators yearning for an arrow from some political cupid. The emotionalism and commitment that is the soul -- not to mention the fun -- of politics is sorely missing. Democrats are picking their candidates as they do their accountants. The word "competence" gets thrown around a lot.

Cuomo knows all this. He knows, too, that the economy might be on the verge of a breakdown. If that's the case, he would be poised, like a previous New York governor, to take over from a Californian -- Franklin Roosevelt from Herbert Hoover. A second New Deal is a tantalizing prospect. Even better, rumors that Cuomo's in-laws have Mafia associations have been put to rest. A New York magazine article by investigative reporter Nicholas Pileggi could find no basis for the stories. In Mafia parlance, Cuomo was unmade.

But the duty Cuomo says he would owe his party and the nation if called upon to, say, break a convention deadlock is not just a prospective one. It exists now. There is a palpable yearning among Democrats for a candidate with the presence and charisma of a Ronald Reagan -- for someone who fills a room by just entering it. For the moment, Cuomo is that man. But that perception may be based more on longing than on reality. No one knows how Cuomo would do as a national campaigner -- whether his temper, pride and sensitivity would diminish his stature. The New York governor has his petulant side, to say the least.

In the old days, just being governor of New York was enough to qualify a person as a presidential candidate. That's no longer the case -- nor should it be. Governors lack foreign policy experience. But aside from that, no party should choose a nominee who has not proven himself on the stump. The virtues of campaigning are much overrated, but they exist. No one wants a Cuomo who in a general election campaign turns out to have been a mistake -- a prideful, insular man whose ideas, character and personality were tested too late.

Even his critics concede the promise of Mario Cuomo. For many Democrats, he is the ideal candidate. But ideals are often unattainable -- which is what makes them ideals in the first place. Cuomo has played that role perfectly -- tantalizing and remaining aloof. It's a game he seems to enjoy, but -- for all his sincere indecision -- it's a selfish one in which he has it both ways. He owes it both to his party and to the nation to stop doing a Milton Berle routine. Only one hand should stay up. If he's serious about his proclaimed duty to the nation, it ought to be the one that means a presidential effort.