An unexpected development at the Democratic convention was the emergence of Gov. Mario Cuomo as a political star. Delegates were casting him as a potential standard-bearer. They were enthralled with him. But the talk was of Governor Cuomo in 1988 - not 1984 - although many were saying privately that the New York governor stood the best chance of beating President Reagan.
Walter Mondale's prospects have improved immensely as the result of a convention that brought many Democrats back to their party. The addition of Rep. Geraldine Ferraro to the ticket played particularly well around the country. And Mr. Mondale himself made the best speech of his career.
There was a period - before presidential primaries had become part of the nominating process - when a convention, moved by the eloquence and political appeal of a Cuomo, might have turned to him to lead its ticket.
That was the time of the boss-controlled conventions, before the process was opened up and democratized. But those bosses, whatever may be said against them, were attuned to one factor: They wanted a winner. Their own jobs and how well they prospered depended on finding a winner. Thus, if the bosses concluded that, say, Mr. Cuomo might beat Mr. Reagan and that Mr. Mondale's prospects of victory were less bright - they might well have met in a ''smoke-filled room'' to see to it that the New York governor prevailed.
A lot of the bosses would already be committed to Mondale. But they could be more flexible than the delegations that make up conventions today. That is, in those bad old days Cuomo might have caused a convention stampede in his direction that could have ended with his nomination. It could have happened then. But not now.
Those candidates who went through the process that preceded the Democratic convention might well say that Cuomo did not deserve the nomination and that the primaries were the true measure of how the voters felt about whom they wanted for president.
But a relatively few people voted in the primaries. Should that small segment of the voters be allowed to lock in delegates at the convention? Furthermore, hasn't this resulted in an inflexible, closed convention? And if that is true, has the nominating process truly been democratized? Theoretically the delegates could have moved to another candidate. But it was obvious that delegates are bound by loyalty to the candidates they have represented in the primaries.
When Wendell Willkie took the GOP nomination away from the Republican favorites, he did it by the overriding appeal of his personality and his compelling message, and by packing the balconies with supporters. The GOP leaders thought they sensed that Willkie was the choice of the delegates and Republicans everywhere. So they rallied behind him. But today a Willkie - who went on to wage a terrific if losing campaign against the unbeatable Franklin Roosevelt - would not have a chance of turning a convention in his favor. Cuomo's performance was electrifying. To some observers it did seem such a shame to let him go back to New York when he clearly seemed poised to take the nation by storm.
But could he have remained the Cuomo of San Francisco - the star that glowed so brightly there? As some wag said, ''Cuomo's was a hard act to follow - even by himself.'' Doubtless his campaigning would be compared with that peak performance, when he held the convention and the public in his hand. As the nominee he could have turned out to be a disappointment.
His was a fresh face on TV. Someone has written that the shelf life of anyone who is continually on television is about three months before people begin to tire of him or her. It is arguable, however, that Cuomo's fresh appeal might have extended as far as the election.
Whatever. The point is not how well Cuomo would actually do - or if he and not Mondale should have had the nomination. It's just that the present convention process doesn't permit such refreshing spontaneity to take place.