Every experiment should show such felicitous promise as "From Cleveland," a CBS comedy project getting a trial airing tonight at 11:30 on Channel 9. This inarguably happy hour is the product of bright minds and brave hearts which obviously harbor some mysterious lingering respect for television -- late-night television, anyway.

It's a celebration, in its way, of late-night America, of urban folk-culture, of joints and dives and hangouts. Producer Rocco Urbisci's idea is to stage scripted comedy against actual, if often ignoble, locations, and he has the writers, performers and directors (Bob Bowker) to make this concept click like crazy.

Most of those in the cast are expatriated Second City TV players minus roly-poly John Candy, which is his misfortune. They pop up in such Clevelandian climes as a city square, where orating crazies go through a changing of the guard, and a grade school classroom, where a teacher confronts the parents of her worst students and has no trouble discerning how they got that way.

"You must be Worm-Face," says the mother of one of them while shaking hands.

Tying these and other vignettes together is the running counterpoint of "The Bob and Ray Radio Show," starring those heroically venerable broadcast veterans, Bob Elliott and Ray Goulding. No one can make almost nothing funnier than they can, and their incomparable gift for locating the absurd centers of prosaic situations provies completely harmonious with the younger-generation comedy being performed.

"From Cleveland" was taped entirely in Cleveland, except for the Bob and Ray material, last March and April. Sheerly by the most incredible and meaningless coincidence it was scheduled to air just prior to the upcoming Cleveland presidential debate. Cleveland, oh Cleveland -- could you have but dreamed of such a glorious hour in the moon? And a full moon at that.

Each member of the troupe gets a chance to shine -- Catherine O'Hara as the exasperated teacher; Andrea Maratin as one of those earthy omniscient waitresses; Joe Flaherty as an unreconstituted barfly; Dave Thomas in a wickedly targeted Bob Hope impersonation; Eugene Levy as the world's least-indecipherable cipher.

And they all take turns at Big Al's suprise birthday party, a three-minute tour de force , and an excruciating ordeal for Al.

Bob and Ray, of course, are a repertory company unto themselves, ageless and timeless, and understated to the point of perfection. Seated at microphones in a radio station, they cheerfully bamboozle listeners with an adroitly finessed extravaganza: a jackpot call, interviews with a dentist and a Madagascar animal expert, a "helping hand" to someone in need. Naturally, Bob and Ray are all of them. The quality of hoax is strictly gourmet.

Rod Warren supervised the writing, Allen Rucker was co-producer and those involved not only maintained a high level of quality but also found a fresh wavelength, and made it their own. People who see old Ernie Kovacs shows today may say, "Gee, he wasn't always so hilarious." "No. But what an attitude he had." There's the same consistent sense of pixilated intelligence to "From Cleveland."

It's not a moment too soon to note that there's the potential now for a true comedy renaissance in television. It will probably have to be confined to fringe hours like late-night, when there aren't so many dummies watching. No, not viewer dummies, network executive dummies.

The amount of ambitious comedy talent now available to and even amenable to television is formidable. Take the "David Letterman Show." NBC did. They took it off the air, yesterday, but not before it had showcased attractive and distinctive newcomers including Letterman himself, the hilarious Edie McClurg, Wil Shriner and many others. The show was too hip for daytime, but these people are bound to resurface soon.

The late, great "Saturday Night Live" made all this possible.In future years it will be looked back upon as reverently as Edward R. Murrow is now. "From Cleveland" is the first beneficiary of the "Saturday Night" legacy to show truly original brilliance and strike off in new and uncharted directions.

You can't get much more uncharted than Cleveland. But you can try.