The box office is booming, but who's making tomorrow's movies?

Mixed news from the movie front. On the cheerful side, 1983 got off to a rousing start at the box office. Grosses went up for every recent film in release - in some cases way up. The trade newspaper Variety calculates that a whopping 13 pictures pulled in more than $1 million over the New Year's Day extended weekend. Similarly, the New York Times reports that moviegoers spent some $300 million for tickets during the month-long Christmas season that ended last Sunday.

''Tootsie'' was the champ. More than doubling the take of any other movie, it joined ''Gandhi'' and ''The Toy'' to earn Columbia Pictures an all-time ''personal best'' in weekly revenue. ''The Dark Crystal'' broke the $5 million barrier at New Year's, along with ''Tootsie'' and ''The Toy,'' according to Variety, while ''Best Friends'' and ''The Verdict'' trailed close behind. Also riding high are ''48 Hrs.'' and the unstoppable ''E.T. The Extra-Terrestrial.''

In economic terms, it's nice to see Hollywood selling so many tickets after a disappointing fall slump. And in cultural terms, it's encouraging to note the relatively high quality that marks many of the New Year hits. ''The Verdict,'' an intelligent and superbly crafted drama, is running second only to ''Tootsie'' on a per-screen basis. ''Tootsie'' itself has more depth than most recent comedies, as does ''Best Friends'' with its sharp dialogue and neat construction. Then there's the visual inventiveness of ''The Dark Crystal'' and the timeless appeal of the reissued ''Peter Pan,'' both aimed at family audiences and doing just fine.

This is not to overlook the inept silliness of ''The Toy'' or the fiercely antisocial violence of ''48 Hrs.,'' another current favorite. But the overall intelligence level is comparatively high at the moment, and it's good to see audiences respond enthusiastically.

Behind the scenes, a less positive note is being struck. Despite good news from the box office, Hollywood production has sunk to its lowest level in 15 years, generating waves of unemployment and highlighting a trend toward overseas rather than domestic activity by the major studios.

Hollywood's labor situation in late 1982 was called a ''wasteland'' by union officials, says Variety, with worldwide production down more than 10 percent from the year before. The situation is no better now, with only a half-dozen union-based movies currently shooting in Los Angeles.

In sum, fewer movies are being made, and those that do go before the cameras are more likely to be shot outside the United States. Last year, writes Variety's industry analyst Todd McCarthy, major-studio filmmaking within the US declined more steeply than at any time since 1970. Yet foreign production by the same companies zoomed. While overall production by the ''majors'' went down 16 percent last year, American production fell off 38 percent (the largest change ever felt by Hollywood's labor pool) and overseas production soared by 75 percent. Leading the pack was MGM/UA, which reportedly based 11 films abroad in 1982, compared with only two in the US.

In most years, Mr. McCarthy calculates, the major studios produce about 20 films in foreign climes. The 1982 figure, 35, is the largest number in 10 years. Behind the trend, apparently, is the recession-induced appeal of low labor costs and more-favorable rates of exchange. What effect this may have on the quality of future movies - if the pool of skilled and experienced Hollywood labor now shrinks or simply becomes discouraged - remains to be seen. One producer's philosophy

Though he's a recent addition to the corps of Hollywood producers, Keith Barish has a credo: He believes quality has a place on the movie screen. And he's determined to prove it, using experience gained, not in filmmaking classes, but the business world.

Is he winning his point? So far, it's hard to tell from his own evidence. Though it earned money, ''Endless Love'' was an artistic failure - as Barish himself is quick to say, claiming the project was sabotaged by others who wanted to play up its exploitation values. The current ''Kiss Me Goodbye'' is less vulgar but equally dull, though it is also faring well at the box office. Balancing these profitable but negligible projects, many critics feel, is Barish's production of ''Sophie's Choice,'' the generally praised film version of William Styron's best-selling, though flawed, novel.

Barish entered the movie world after a flirtation with politics and a successful business career that left him ''well off financially, but quite unhappy personally.'' He had acquaintances in Hollywood and decided to make it his arena for a new career that would point in fresh directions while still calling on his business experience. He began financing ''development deals,'' providing funds for potential film projects in their early stages. Later he graduated to full-fledged production financing.

What's the key to success on your own terms? Independence, Barish says. He claims to have no interest in working for a studio, even as chief executive. Independent producers can operate less expensively and more flexibly, largely because they don't have to shoulder the huge overhead costs that hang like thunderclouds over most of Hollywood.

Still, for all his individualism, Barish remains a team player who recognizes the importance of each contributor to an enterprise as massive as a major film. He even acknowledges the primacy of the director, within broad limits. ''It's the function of the producer to help and advise the director,'' he said over lunch recently. ''But that doesn't mean rubber-stamping everything he says.'' It's also wise to avoid collaborating with weak directors who are easily swayed. What's good for the producer's ego may be bad for the finished product.

Barish is very pleased with the movie version of ''Sophie's Choice,'' which was written and directed by Alan J. Pakula, who also served as coproducer. At first, Barish says, there was much Hollywood skepticism over the very idea of filming this turbulent drama about a concentration-camp survivor. But he and Pakula persisted in developing the project. In the process, they toned down the novel's sexual horseplay and eliminated most of its rough language, building a film version that's more restrained as well as more concise, while preserving Styron's central concern with the lingering physical and psychological consequences of the Holocaust.

Central to Barish's thinking is his conviction that ''quality'' is as good a starting point as ''commercial potential,'' even if box-office success is one of your goals. He likes to point out that even huge flops - ''The Legend of the Lone Ranger,'' for example - began as commercial ideas that were expected to rake in piles of money. ''Being commercially motivated is no guarantee of being commercially successful,'' says the producer. ''So why not start from a standpoint of integrity, and take it from there?''

When pressed, Barish admits that Hollywood could well sink into a morass of junk filmmaking, spurred by apathetic audiences and unimaginative producers. It's a struggle to make high-quality movies in the current atmosphere, he says. Yet he believes in the struggle, and hopes his own more ambitious projects will prevent viewers from becoming so cynical they don't even bother to find out what's playing.

Future items on the Barish agenda include ''Modigliani,'' based on an Off Broadway play, and a screen version of D. M. Thomas's novel ''The White Hotel.'' Also in the works are an adaptation of the stage revue ''I'm Getting My Act Together and Taking It on the Road'' and a remake of an Italian film called ''The Misunderstood,'' which Barish saw on a plane ride.

Not commercial, you say? Guess again, the producer replies. Time will tell if his instincts are on target.