No prime-time program now on the air has anywhere near the organic and contagious vitality of "SCTV Network 90," a late-night treasure that is also a hidden treasure thanks to the programming and promotion al ineptitude of NBC.

"SCTV" has been airing after Johnny Carson on Friday nights since May; NBC rushed it onto the air in the hopes of making some numbers in the May sweeps, having failed dismally for years in the period with the laggardly "Midnight Special." Only last week, though, did it occur to NBC to advertise "SCTV" during the Carson show that percedes it.

But the program has lured the kind of cult following that first glommed onto "Saturday Night Live" when that show hit late night like a tornado in 1975. To compare the two programs is slightly risky, since the comedy styles are different, but basically, "SCTV" specializes in the kind of enlightened satirical slapstick that "Saturday Night" in dulged in only occasionally and sometimes reluctantly; at their best, the SCTV players, who are all writers as well, rise to dizzy, delirious heights of inspired and malicious whimsy.

There is about the program something rare now in television: a true sense of merriment. You get the feeling from watching that the seven talented improvisational actors and the additional unseen writers and producers get together and just beat their brains out thinking up funny stuff. Their batting average is admirably high and so are their spirits on the air.

Thus on a recent Friday the SCTV players test-drove a TV version of a mythical tabloid, "The National Midnight Star," whose cover story on Erik Estrada was headlined, "CHiPs Star Admits, 'Aliens Fixed My Teeth.'" Among the scoops: "Jack Benny's dungeon was no joke, claims Don Wilson [Benny's announces]. 'It was a torture chamber and I spent many a night on the rack.'"

An alert busboy was credited with crudely shot film of Henry Kissinger running drunkenly amok "at a posh Washington restaurant" and ripping the dress off a lady diner. "Also present at this restaurant," said the story, "was comedienne Carol Burnett, who told Star reporters, 'Kissinger was drunker than I've ever seen him, and I've seen him drive limos backwards through car washes.'"

What the gang parodies, ridicules, bombs and strafes most often is show business bad taste, of which there is a bottomless well of source material. Joe Flaherty, the oldest of the troupe ("in my late 30s") says he recalls wondering aloud to cowriter (and National Lampoon alumnus) Harold Ramis after the show's first season as a syndicated series, "Is there that much to parody?" and Ramis shooting back "Yes! You could do it ad nauseam."

Flaherty, like the others in the cast, plays many roles, some of them recurring. Among the most prominent of the regulars he plays is Guy Caballero, owner of the fictitious SCTV network and in Flaherty's words "a real cheap Lionel Barrymore." Caballero dresses in a three-piece white suit, and although he can walk, he spends most of his time rolling around in a wheelchair in order to inspire "respect" in underlings.

Caballero can go schizophrenically from polite palaver to a bullying bark; he began the first NBC edition of "SCTV" by inviting viewers to "sit back . . . SHUT UP . . . and enjoy the show."

ythe other regulars: Catherine O'Hara (a.k.a. Lola Heatherton, the talentless chanteuse whose every performance amounts to open-heart surgery on an audience); scene-stealing John Candy (Johnny La Rue, candied ham); the brilliantly versatile Andrea Martin (hot-to-trot station manager Edith Prickley, or imcomprehensible immigrant Pirini Scleroso); Eugene Levy (quintessentially nerdy Mel Slurp, host of the ragtag "Mel's Rock Pile" dance show); Rick Moranis (Gerry Todd, world's first video deejay); and Dave Thomas (constantly contentious but eminently corruptible Bill Needle).

The "SC" in SCTV stands for Second City, originally a Chicago improv club (out of which came some of the original "SNL" regulars) which has branched out into franchises; most of those on the SCTV show, which began as a monthly half hour in Canada in 1976, are from the Toronto chapter. Of the seven on-air performers, all but Flaherty (from Pittsburgh) and Martin (Portland, Maine) and Canadians.

Dan Aykroyd is Canadian. Lorne Michaels, producer and creator of the original "SNL," is Canadian. Is there a renaissance, or just plain naissance, of Canadian humor? Flaherty says no. "There are 10 funny people in Canada, and we've got all of them. Actually a new wave or something came sweeping over in the early '70s."

NBC got wind of the show after its two successful years in late-night syndication (it is still seen in many markets, including on Washington's WRC-TV Saturday nights at 1 a.m.) and managed to cut a real cheap deal for itself, budgeting each weekly 90 minutes at $150,000, about 100 grand less than the producers need. Even as we sit here, you reading and me writing, NBC executives are haggling over costs before agreeing to pick up the show for the fall season.

They've been hemming and hawing for weeks. The SCTV players sit up there in Toronto writing the scripts and then fly off to video facilities in remote and bleak Edmonton for the weekly tapings. They would prefer the show be only an hour -- and in fact, they're lucky to come up with 30 minutes of Class A material in each 90-minute program -- but NBC demands the longer format.

The network has sunk millions into trying to keep "SNL" alive -- from all evidence, a hopeless task -- and the logical thing to do, it appears, would be to ditch "SNL" altogether and move "SCTV" into its time slot. O'Hara, a beautiful and multidexterous actress (who, as Lola, will tell a cheering audience, "I want to bear all your children") says she's heard rumors that such a switch is in the making, but apparently they are groundless. NBC insists a third revised "SNL" will debut in October.

O'Hara was to be a member of the new trouple on that show. But she spent a week with them in New York last spring and then hit the road back to Canada. "I was really afraid of its trying to be the third 'Saturday Night Live,'" she says from Otonto. "They kept telling me, 'No, it's going to be different,' but what they really wanted was to get back to what it was. I felt I didn't belong, like an outsider. I said, 'Aw-oh. I made a mistake.'"

She didn't actually pattern her Bolla Lola after Joe Heatherton, O'Hara says. yshe had never seen Joey Heatherton. "I just did the worst delivery of lines I could think of. Then I finally saw Joey Heatherton in one of her films -- and I had been doing it exactly like her!" Now she's intent on working up a satire of dewy-eyed TV evangelist Tammy Bakker. "She cries every single time she's on camera."

yin order fully to appreciate SCTV's accurate aim, you really have to be a fairly hearty TV- watcher -- not just of network prime time, but also a wayfarer in those seductive, scuzzy fringe periods and UHF stations that are like the frim outskirts of Baltimore. The SCTV people play it all back in a time warp, so that Merv Griffin, normally beamed in "From New York, From Las Begas" and so on, one week emanated from Mayberry RFD and became "The Merv Griffith Show," with Merv mooing and cooing over Aunt Bee, Opie and ever-whiney Floyd the Barber.

One of the most conceptually ambitious TV sketches ever was SCTV's "Play It Again, Bob," which depends for effect on one's knowing that Woody Allen once expressed admiration for the comic timing of Bob Hope. In this sketch, patterned after the Allen movie "Play It Again, Sam," each comedian co-opts the other and the sketch becomes some kind of double-whammy parody.

It helped, in that case, that Moranis does a letter-perfect Allen impression and that Thomas captures Hope the way no one ever quite has. Thomas even showed a tape of the sketch to Hope, who didn't get it, but told him, "Hey, you got the voice." Wild.

Occasionally the SCTV team gets shrill, or obscure, or they refuse to let go of a bad idea ("Mrs. Falbo's Tiny Town"). But they ransack the pop-cultural attic of the nation for targets that nobody else goes after -- yodeling Slim Whitman, or blithering Richard Harris, or punk-rock commercials ("Poochare. It's dogfood. It's now") or, in a recent and gratifyingly devastating hoot, blank-eyed Broke Shields (O'Hara) and her showbiz mother (Moranis), who had inexplicably been given a talk show of their own.

Television richly deserves what the SCTV ensemble does to it. It may even be worth sitting through much of TV's excruciating imbecility to get to the SCTV parodies as a payoff. ythe show used to begin with countless viewers heaving their TV sets out the windown in disgust; watching the program offers the vicarious pleasure of doing that without having to wrestle with the repair bills. Finally, "SCTV" increases one's appreciation of television, if primarily for the service it does in giving all of us something to kick around. On "Network 90," the kicks are swift and, often, sublime