THE NEWLY announced Carnegie Commission on the future of public broadcasting offers hope that public TV may finally find means of solving some of its chronic difficulties. The previous Carnegie Commission on "educational" television in 1967 resulted almost immediately in basic legislation - the Public Broadcasting Act of 1967, which set up the present system and which, for better or worse, enabled its phenomenal growth over the past decade. The new commission, funded at $1 million by the nonprofit Carnegie Corp., and scheduled to issue a final report early in 1979, has strong presidential backing.

We'll never have public television in this country more to everyone's liking, however, until we acknowledge that we've been demanding the impossible:

We wanted it to be "better" than the commercial variety, but at a piddling fraction of the cost.

We asked that it be free of governmental pressure or influenced, but have filtered its funds through political appointees (the Corporation for Public Broadcasting).

We've desired it not to be too dependent on federal financing, but we object to its marathon appeals for audience contributions.

We've looked to it for vital new ideas and "experimental" approaches, and then complained about the "elitism" of offbeat programming.

We've urged it to explore local and minority issues and interests, and then bemoaned its lack of broad national appeal.

We've pined for the encouragement of bright, young, creative talent, but reserved our adulation for BBC period dramas like "Upstairs, Downstairs."

At the root the contradiction is a paradox in our thinking about public television - too often, we judge its performance by the same criteria we apply to commercially sponsored TV, i.e., numbers of viewers. If what we're really after is an alternative to network pap, we have no business looking for mass appeal at the same time. If what we're more concerned with is vast viewership, then esthetic and intellectual standards will have to be compromised. We can't have it both ways at once. Maybe new technologies like satellites and cable will help - but it will have to be by plan and intention, not accident.

The announcement of the new Carnegie Commission was accompanied by a statement from President Carter, who said in part, "I welcome this effort to improve the quality of television for millions of Americans." A laudable sentiment, and hardly a spur for controversy. But what exactly does "improve the quality" mean? That we should have programs like "The Ascent of Man," but, somehow, with ratings and shares equivalent to "Charlie's Angels"? It is one thing to underestimate the intelligence of the average viewer, and quite another to suggest than in a populaity contest between Jacob Bronowski and Farrah Fawcett-Majors the former would ever run even a close second.

One is led to a similar quandary by this statement in a recent New York Times editorial: "The dependence (of public TV) on imports, particularly from Great Britain, raises the question of why America's broadcasters do not produce more impressive programming of their own." What does "more impressive" mean here? That American producers should be mounting glossy, expensively costumed historical soap operas for domestic consumption, and pray for viewership to compete with network game shows?

Our own public TV has already come up with a dramatic series, "Visions," that was far superior in artistic worth and creative ambition to anything ever to come from the BBC, and if it failed to make as big as a dent on public consciousness as "Lavern and Shirley," or "The Pallisers," for that matter, it was assuredly not for lack of "quality." When was the last time you saw a British program based on an original script, not conforming to serial formulas, and dealing with great substantive human or social themes?

There is a simple answer to the Times' question. Compared to the costs of original production, the purchase of already canned imports is a raging bargain.Public television relies on the British stuff because under existing funding limitations, it cannot affort to produce its own, except once in a blue moon and a relative shoestring. And if "impressive" programming is part of the requirement, the costs fly out of sight. Why should first-class writers, directors, actors, filmmakers, composers, musicians or journalists work for public TV for peanuts, when they can soak the profit-laden commercial networks for colossal fees?

The real wonder about public television in this country is not that it has been doing so badly, but that it has managed to do as well as it has in the killing noose of its penury and bureaucratic hassles. On the cultural front alone, there has been nothing on commercial TV or BBC imports either to remotely match such series as "Visions," "The American Short Story," "In Performance at Wolf Trap," "Theater in America," or "Dance in America," all domestically produced within the past several years.

Perhaps the future of public TV is dependent on a truthful recognition, once and for all, that not everything popular is necessarily good, and that, conversely, not everything good is necessarily popular. We willingly pay tax dollars to keep in our public libraries tomes on differential topology or Sumerian agriculture, not because they'll be consulted by millions of people, but because their intrinsic value as knowledge makes them treasurable.

There's no reason not to regard television in the same light. The recent, superb "Trailblazers of Modern Dance," for example, may only have been watched by a "small" audience of a few millions, the first time around. A hundred years from now, however, if we're smart enough to preserve it, it will still be as pleasurable and enlightening. About how many segments of "The Forsyte Saga" or "Baretta" can such a claim be made?