There's no discernible thematic trend to this year's New York Film Festival, which opened here Friday night at Avery Fisher Hall, but it seems to be generating more than usual enthusiasm among film buffs for the sheer number of "name" directors represented among the entries, with an emphasis, as usual, on foreign-language features.

Francois Truffaut, who's frequently had the New York Festival as an American launching pad, is contributing his "The Green Room," starring himself and Natalie Baye and based on a Henry James story about preoccupation with death. Claude Chabrol, Rainer Werner Fassbinder, Jerzy Skolimowski, Eric Rohmer, Bertrand Blier, and Krzysztof Zanussi are among the other overseas directors on the roster, along with playwright Peter Handke, in his debut as a film-maker.

There'll also be the customary handful of promising first features by asyet unknowns, such as Canadian Zale Dalen's "Skit Tracer," about a single-minded loan collector and from France, Luc Beraud's "Like a Turtle on Its Back," a comedy about writer's block; a couple of notable revivals including the newly reconstructed, three-hour version of Fritz Lang's 1928 "Spies"; a special sub-series on new Japanese cinema; and a smattering of shorts and documentaries.

American directors are represented too, including Martin Scorsese and Robert Mulligan, and though the idea of the festival is primarily to introduce films beyond the usual Ken of commercial distribution, this year's selection committee, headed by Richard Roud, voted somewhat surprisingly to go American and populist for the opening too, with Robert Altman's new "A Wedding,"

One of the few unassailable things that can be said about Altman is that when he turns his attention to a subject - Korea medics in "M*A*S*H," country music and political campaigning in "Nashville," psychology of the sexes in "Three Women," for example - you know he's been there. Whether you adore or despise "A Wedding," (and this picture, like his others, is apt to divide audiences and critics into antipodal camps), you won't easily forget his raucously satirical view of the matter.

"A Wedding" is only a few minutes over two hours long, but it feels vast and fatiguing, like the plush, sprawling marital fiesta it chronicles. In this respect, Altman has fulfilled his aim. He said he wanted audiences to have the sensation of having been actual guests at the event.

The film is Altman's attempt at a "Nashville" of the nuptials. Yet for all its scope and bravura tactics - the 24 "major" characters of "Nashville" have become 48 in "A Wedding" - the movie is oddly flat and hollow in impact.

The difficulty is Altman's attitude toward his characters. Every last one comes across as more of a caricature than a person, and the film as a whole impresses one as a jaundiced cartoon, rather than a comic vision of American tribal customs. It's as if Altman really set out to make a sitcom, the people functioning as mere scaffolding for a barrage of grungy gags. Altman seems curiously ambivalent about his fellow humans. He's obviously fascinated by them, but they inspire no affection in him. Instead, he's fixated on what he takes to be their universal venality, crudity and corruptibility.

"A Wedding" encompasses a single day that begins with a church ceremony which unites the daughter of a nouveau-riche Southern trucker to a military academy graduate, scion of a Midwestern clan of Italian-American aristocrats, and proceeds through a lavish reception at the groom's family mansion.

From the start, skeletons come tumbling out of closets in an unceasing horde. As the wedding party wends down the aisle to a Bach organ prelude a teen-age usher chews a wad of gum in a closeup. The presiding bishop is a senile dodderer. The bride wears braces on her teeth during the ceremony. The bride's sister is a pregnant slut. The family doctor is a lush with a fetish for his female patients' chests. This relative is an addict, that one a dumb redneck, another a cliche-spouting "radical." Everyone is carrying on in the buses, from the gardener to the bride's mother.

At one point towards the end, it seems as if Altman is bucking to become the Ken Russell of American film, as the movie cuts from a revelation of male homosexuality to one of lesbianism, the security guards mistakenly beat up an Italian relation, the bride's brother has an epileptic seizure, and the sports car presumably transporting the newlyweds is consumed in the flames of a hideous collision.

In his ermarkes after a press screening and from the stage on opening night, Altman insisted repeatedly that it would be a mistake to look for "meaning" in "A Wedding," that it was "just another movie," not to be taken seriously, and that the audience had best "giggle and give in."

But it's hard to see what there is to laugh at, if you don't happen to find the spectacle of a wholly unappetizing slew of characters making pigs, gluttons and asses of themselves particularly amusing. As for the "essay" aspect, it is less revealing of American mores and foibles than it is of Altman's misanthropy.

It's quite possible, however, to remain unpersuaded by "A Wedding" and still admire the ambition of Altman's concept, the splendidly controlled anarchy of his direction, and his precoity both with the movie medium and with actors.

Though the portrayals inevitably broder on travesty, there is brilliance and skill in Carol Burnett's oafish mother of the bride, Lillian Gish's fading matriarch, Paul Dooley's thin-skinned Southerner, Vittorio Gassman's volatile patrician, Howard Duff's blase doctor, and John Cromwell's blithering bishop. These performances, among others, helped give a lift to the festival's flamboyant but otherwise dispiriting inaugural.