ONE OF THE zingiest treats of the new TV season was going to be all about the new TV season-- and about how television affects American life, which it does beyond all hope. Megan Williams and Nick De Martino, two bright young independent producers, wanted to do a nonfiction hour of public TV that would examine the kookie, nutty world of Nielsen ratings, network brinkmanship and the inscrutable chemistry of TV success.

But they found themselves in another kookie and nutty world -- the world of public television, where decisions are harder to come by than peace and quite in Nicaragua. "Television City," the show they wanted to do, has become The Epic That Never Quite Was, and after two years of jousting with paper shufflers and naysayers within the public TV establishment, too. But the producers still have a show, a healthy half-hour special called "Sit-Com," and it will take viewers into the reality behind the scenes at the most lucrative TV fantasy factory in Hollywood, Paramount Studios.

"Sit-Com" is tentatively scheduled for public TV stations the night of Wednesday, Oct. 3. It isn't as magnum an opus as the producers planned; they wanted to include, among other features, a live, national phone-in reaction to the new season that would challenge the accuracy of the omnipotent Nielsens. But it does offer fascinating backstage peeks at TV professionals who create hours and hours of foolish junk that each week captivates a nation.

This isn't just run-of-the-mill junk: This is the creme de la dreck, shows like "Happy Days" and "Laverne and Shirley," two goldmines that have earned millions for ABC and that will have, in syndication, a lifetime earning power estimated by one Paramount executive at $400 million.

Think of it. No, don't think of it. It's too depressing.

Garry Marshall, the man who created these programs and others like "Mork and Mindy," never need work again to remain a millionaire for life; but that doesn't keep him away from the Paramount lot, where he can be seen roller-skating from soundstage to soundstage and where he renegotiates his contract largely to demand cheap frills like a private basketball hoop, so bored is he with his fabulous success. There is no more successful producer in all of television if success is to be measured by money-- and in television, it's measured by nothing else.

De Martino and Williams have high praise for Marshall and the generous way he cooperated with their project. But the sad fact is that Marshall is the man who set television back at least 10 years. He steered situation comedy away from the bold new directions pioneered by Norman Lear and MTM Enterprises and reduced it to kiddie pap and soda pop -- strictly predictable physical simplistics and slick hick shtick. Few have done more to make the television of the '70s undistinquished.

Sitting in a grubby basement editing room two blocks from Paramount and right next door to Nora's Massage Parlor ("Ladies Only"), Williams looks at some of the rough footage from the show. On her TV screen we suddenly see Marshall joining director Jerry Paris for the ritual Throwing of the Candy Bars into the studio audience at the filming of the first "Happy Days" of the season. Marshall gives all his audiences a mid-show "candy break" to boost their energy levels so they'll laugh loudly on the soundtrack.

Former U.S. senator John Tunney is among those sitting on bleachers and grabbing at candy in that audience and he exclaims, "I love the show, the show is great," which helps explain why he is a former senator.

In another scene, the ABC censor assigned to "Happy Days" declares, "I like being a censor." And says, "We're super-sensitive people." But Marshall and his staff can be seen later going over a list of largely ridiculous censor's demands, including the deletion of a pasty reference to "oil companies" in a "Mork and Mindy" script.

Outdoors, on hot Gower Street, Williams and the crew interviewed people waiting for the privilege of sitting in the studio audience and being thrown sweets like monkeys in a zoo. "They talked about how the shows they were going to see insult their intelligence, but there they were standing in line, waiting to get in," Williams marvels.

What comes across in much of this footage is an evanescent kind of sadness that hangs over Marshall's phenomenally successful manufacture of mass mirth. Henry Winkler, just back from summer hiatus and wearing a beard, looks disillusioned and remote in footage shot at rehearsals. His attempts to become a movie star were an enormous flop and there he is, trapped in the skin of the Fonzie that made him famous; when he sheds it, he is nothing.

And when the "Happy Days" cast members come out in their funny costumes to take bows after filming is over, they look pathetic, like a pack of hapless cut-ups in a high school talent show. As Penny Marshall and Cindy Williams rehearse a ridiculous fight with giant pitchforks for a future "Laverne and Shirley," you can't help wondering why 50 million viewers go bananas over this, why this slender sort of whimsy is enough to make America laugh, why so many people should be making so much money on such minimally imaginative creations.

And whether they don't feel at least a little bit ashamed of themselves.

For Williams and De Martino, the faintly demoralizing cynicism of bigtime network TV doesn't seem quite so frustrating as the two years they spent getting their show through the voracious meat-grinder of public TV bureaucracy. If you happen to be the BBC, it is easy to get any old thing on American public TV. If you are an independent American producer with a great idea -- or, worse, a new idea -- every conceivable obstacle will be thrown in your path. This may be the most clumsily run television system in the world.

De Martino says some officials at the Public Broadcasting Service (PBS) were consistently supportive and helpful (though typically timid PBS lawyers warned against possibly offending the commercial networks with the show, as if that should matter), while over at the skinflint Daddy Warbucks of the system, the Corporation for Public Broadcasting (CPB), diffidence and indecision were having their usual field day. One gnome with veto power huffed that the show was "not a prudent expenditure of public funds." After all, how important can American television be? Only about 100 million Americans watch it every week.

In desperation, De Martino and Williams, who have a 3-inch-deep file of correspondence and proposals concerning the show, approached Time-Life's pay cable network, Home Box Office, and were greeted with initial enthusiasm. Then, however, director of original programming Iris Dugow told them, "We have to audience-test this to see if people will respond to your subject." Apparently Dugow hadn't heard that 98 percent of all U.S. homes have at least one television set and that the average set is on more than 6 hours a day. The inner workings of a medium that preoccupies and permeates the lives of so many people could surely be counted on to interest scads of them.

Eventually HBO said no because they were afraid of plugging ABC shows. In point of fact, HBO, which advertises itself as something "different" for cable viewers, is trying to develop its own sit-coms, just like those of the commercial networks, except they will probably be dirtier.

Finally, PBS came up with $15,500 to start production of the show -- a year after the initial proposals were filed -- but only authorized a "demo reel" of producer Marshall in his habitat. Williams and De Martino thought this insulting to the obliging Marshall, and were able to get another $5,000 so they might come up with a half-hour's worth of footage. But then that $5,000 was eaten up by union problems that arose when their videotape crew arrived at the Paramount lot: Reigning unions demanded that two extra people be added to the crew.

More money was found and then the idea of a partly live, one-hour show arose. This program would air the first Sunday night of the new season and immediately sample the nation's reaction to the new programs. A phone-in voting system could determine how many people had preferred "Mork and Mindy" over the competition. A studio audience could give its own instant reactions to the shows. A major-name host (Phil Donahue was mentioned) could emcee the show. It might have been a fresh, comprehensive look at television and the people who watch it and make it -- the kind of thing you never see on television -- but De Martino simply wasn't able to raise the money in time for the early September air date. The producers went back to their half-hour format.

De Martino does not see the public TV situation as hopeless, just exhausting. "Some good people inside those weird institutions were trying to slug it out for us," he says. "What it all illustrates is not only the complexities of public TV funding, but also how it's almost impossible to get the subject of television on television. It's insane."

The battles are not completely over; lawyers at public TV stations which contributed funds are arguing over whether it is to be "a production of Television City in association with KCET and WNET" or "a production of WNET and Television City in association with KCET" or what. In fact, late last week, officials at WNET in New York suddenly discovered they couldn't find anything on paper to authorize that station's share of the show's production costs. Station executives, and De Martino, were naturally hoping something will turn up.

Television, television! Such a business.

Among the many changes the program went through was an assortment of titles -- "Beat the Nielsens" and "Television City" both losing out to "Sit-Com." One of the best titles was suggested by Los Angeles filmmaker Alan Rucker. He told Williams they ought to call the show "Laughing to the Bank."