A slice of life, a piece of perfection, another Frederick Wiseman film for public television: "Racetrack," shot in and around Belmont Park and airing at 9 tonight on Channels 26 and 22. The latest of Wiseman's impressionistic immersions in an American subculture, the film demands to be taken on its own terms and, on those terms, is fascinating.

Part of Wiseman's video ve'rite' technique is to strip film clean of extraneous clutter and the tidying organizational techniques that most documentary filmmakers use. And so there are parts of the film that are hard to follow, and people whose precise identifications remain unclear. It doesn't matter. This is a work of informational art that tells its story in distinctively televisionary syntax.

Many varieties of human folly implicate and exploit the lower animals. The first glimpses of horseflesh in "Racetrack" are of the graceful beasts in a natural habitat, roaming, as it were, in a gloaming. That is the last glimpse of anything remotely resembling a natural habitat in the film.

Wiseman shocks us into the artificial world of horse racing with two discomforting introductory sequences. The first is a graphic, and prolonged, film record of a mare giving birth, with race track personnel playing midwife. The second, and considerably more startling, is a breeding sequence, the definitive hurried courtship, with race track personnel playing, well, not Cupid exactly. More like pimp.

One is reminded of what Shaw wrote: "I know two things about a horse; one of them is rather coarse."

"These are very sensitive animals," says a woman track announcer who sounds like Gilda Radner's Baba Wawa (later, a track official leading an employe discussion group sounds like Don Novello's Father Guido Sarducci). She hails them with the insulting compliment that they are "professional athletes in every sense of the word." Horses are made to serve the strange human need for competition and games of foolish chance.

Wiseman wanders around Belmont finding ripe, illustrative material, most of which fits into the abiding themes of his films, the melancholia peculiar to industrial societies, the emotional wages of materialism. Horse racing is a small industry, comparatively, but it serves as a rich microcosm. Various strata are contrasted, but almost everyone looks a bit silly.

In addition to the birth and mating scenes, there is one other harrowing segment. In the second half of the film, a horse undergoes a leg operation. He is anesthetized with an injection -- collapsing, boom, in an instant -- and a tube is shoved down his throat. Then a team of serious-looking surgeons affixes a metal brace to an exposed bone. The postoperative period is a trifle rambunctious.

All this so the horse can continue to race for its owner and the diversion of the race-going public.

Behind the scenes, jockeys lounge in the locker room, watching twin TV sets on which they can see either a camera's-eye view of the track or "The Price is Right." A track official holds a press conference and lauds a documentary he has seen about racehorses. "It's a super, super film," he chimes.

And in a vignette so ideal for Wiseman's purposes that it might as well have been scripted in advance (but certainly was not), a priest at the race track chapel preaches a sermon on the difference between pleasure ("fleeting") and joy ("enduring"), pausing to consider causes of depression. "Depression can come about because of too much television," he says. "So often, television disappoints us and disillusions us. It makes us feel empty and unfulfilled."

Tell me about it!

The priest says, "Life is rushing by and sometimes we wonder whether we grasp its meaning," which Wiseman uses as a cue to cut to the highway outside. It takes us to Manhattan and to Roseland, where a gala racing evening has been planned to honor a 90-year-old Belmont patriarch, or, as the master of ceremonies describes him, "one of the great men of our time, John A. Morris."

There is a sweet banality to "these proceedings," as Morris himself refers to them when he ambles up to make his acceptance speech, prompted along by his wife Edna, who beams. You can feel Wiseman mellowing. He doesn't mean to denigrate these people or this strange silly passion to which they have surrendered themselves. He only wants to find the resonant absurdities in it, and does.

Wiseman can make anything look enigmatically sad -- a sign that says "snacks" at the race track, or a quick glimpse of the girl behind the hot-dog counter chanting to the customers the discouraging words "No beer. No beer." The film was shot by John Davey, but it is producer-director Wiseman's editing that sharpens the images through juxtaposition.

Many of those images are worthy of Cartier-Bresson in their irony and understated poignance.

"Racetrack" was shot in 1981 but attention to other projects delayed Wiseman's finishing the film until this year. He was also distracted, alas, by having to run around in search of production funds. Wiseman's films never grovel, and Wiseman shouldn't have to, either. God knows there's no surplus of original artists working in public TV. You'd think Wiseman, on the basis of his record, would have carte blanche.

But the Reagan-dominated public television bureaucracy would deny composing paper to Beethoven and canvases to Picasso. The pursuit of excellence in public television has fallen to a priority of zero.

"Racetrack" is difficult viewing at times, but then the trouble with most television, public and private, is that it's much too easy. In focusing on a specific, quixotic, rather pixilated environment, Wiseman emerges with a new assortment of insights and observations, and that "Racetrack" could never be adequately summarized in print is part of its brilliance. It's a super super film, from a super super filmmaker.