IF YOU WAIT long enough, someone will finally say something sensible. That's one of our cheerful premises, anyway, and it was borne out last Sunday on "Meet the Press" when Sen. Gary Hart of Colorado got into the raging argument over whether or not Jimmy Carter is a liberal. Merely to stat the subject of the dispute, you will notice, is somehow to reveal, in all its majesty, the absolute foolishness of it. A lot of people seem to think this folly lies in trying to pin down the politically undefinable Mr. Carter. But Sne. Hart understands that that is only a small part of the problem. The tough part is trying to pin down - if, in fact, it really matters - the meaning of the term "liberal."

We will be frank to say that we don't see that it really matters. Any term that takes that much trouble and contention to define is not much of a standard to measure people by anyway. As Sen. Hart observed, what is really going on in the internal strugglings of the Democratic Party, which have engaged the White House, the Congress, the labor unions and various other participants, is in large measure a generational dispute. Thus:

I think it is between those who have espoused the traditional New Deal approaches to social problems and economic problems, as opposed to those who are coming into public office in the Congress, in governorships, in state legislatures around the country who are attempting to question some of the premises upon which the Democratic Party has operated . . . and by and large this country has operated for the last 30 or 40 years, and I think that is where the division is coming. It does not fit in the traditional liberal-conservation categories.

Sen. Hart described one of the issues dividing the political generations as "whether government in fact can solve all the problems." Another is how government should spend - how much it should spend and on what . . . and in what order of priority. There was a time, and not so long ago, either, when great numbers of people who identified themselves as liberals regarded it as vaguely illiberal even to entertain these questions. Government was assumed by them to be overwhelmingly benign in its social ministrations, and there was plenty of money for it to use to put society right, if only a right-wing Congress would let it.

If you want to make a useful division among Democrats and do a little relevant categorizing, you could do worse than to make a distinction between those whol do and those who don't recognize that there are limits to both the money available to spend and the wisdom with which the government in peoples' lives, even for a benign purpose, always so benign in the way it works? Have we not learned that there can be a streak of ugly authoritarianism in even the most well-intended government programs? Can liberals afford to be as contemptuous as they traditionally have been of those who regard inflation as the principal public enemy? Surely, these are the questions that serious-minded Democrats are thinking about just now - not whether it is illiberal of Jimmy Carter to have delayed the prospective introduction of health-insurance legislation until early in 1978.

Jimmy Carter tried to answer some of the criticisms in his speech to the United Auto Workers convention in Los Angeles yesterday. He listed an impeccable array of social and economic goals he hopes to meet. But he also refused to back off the cnetral premise of his domestic effort so far. "We cannot afford to do everything," he said, by way of explaining the obvious - namely, that the country must make some "hard choices." On that we think he is dead right. We also think it would be the final and complete ruination of liberalism - whatever that may mean any more - if its self-professed minions refused to face up to the difficult domestic choices and just kept on asking for it all.