NBC breaks out in benign sequelitis this weekend with three comedy specials that are follow-ups to previous comedy specials: "Twilight Theatre II," in the "Saturday Night Live" time slot at 11:30 tonight; "TV's Censored Bloopers No. 4," tomorrow at 9 p.m.; and "New & Improved: Television's Greatest Commercials II," tomorrow at 10 p.m., all on Channel 4.

By far the best of these is "Commercials," a sparkling hour of memories, magic, sheeer ener-geeee and fast fast fast relief from the usual entertainment programming. The program is even better than the first "Commercials" special, which was considered a risky venture when producers Joie Albrecht and Scott Garen made it (for Carson Productions) last season but which was the top-rated show in the country the week it aired in May.

The examples of TV spots from the past that tumble out sugggest again that commercials are the closest thing to art on television and that those who make them put more wit, imagination and daring into them than those who make the ordinary, not-so-new or improved TV series. "Television's Greatest Commercials II" whirls pell-mell down memory lane; ad campaigns, jingles and characters leap out from the innermost recesses of one's brain and return bathed in cockeyed glory.

For instance, you need only hear a few notes of once-familiar theme music to recognize an inspired campaign for long cigarettes: "Oh, the disadvantages of the Benson & Hedges 100s," a series of comic vignettes that courageously spoofed the product being pitched. Yes, we actually lost something when cigarette advertising was banned from television in 1971.

But the hour is a flood of delights of every commercial kind. Carol Kane stars in a silent-movie parody that turns on cheeky double entendre; having one's first Dr Pepper is equated with losing one's virginity (this was the "Dr Pepper, so misunderstood" era, first strike in the company's drive to shed its image as the favored sodey pop of rednecks and crackers). John Wayne rather movingly rides off into the horizon after a spiel on behalf of California's Great Western Savings. And Mason Reese returns in the full bloom of youth to mispronounce "smorgasbord" for Underwood and earn himself a place in the salesmanship Hall of Fame.

The producers unwisely chop up the Alka Selzter "spicey meat ball" classic (they could do a whole hour on Alka-Seltzer commercials over the years), and sometimes they edit spots into montages so that it's hard to tell where one ends and the other begins. But strangely welcome faces and voices from the past turn up with gratifying frequency: Buster Brown and his dog Tyge, who lived in a shoe; early versions of Jim Henson's Muppets for Wilkins Coffee; John Cameron Swayze doing unnatural things to Timex watches, then getting strapped into a Volvo himself for a commercial parody of a commercial; Boris Karloff selling A-1 Sauce ("Shake some in the stew, Igor . . .") and George Raft starring in a very brief prison epic for, once more with feeling, Alka-Seltzer.

Also recalled are the days when commercials were integrated into programs and sometimes performed by the show's stars. Thus we see Frank Sinatra join Ed McMahon, cohost of this special, in a Budweiser skit; Jack Benny and Ed Sullivan clowning for State Farm; the Three Stooges (after the death of Curly, alas) for Simoniz; Vivian Vance as Ethel Mertz for the Schaeffer Snorkel Pen; George Burns and Gracie Allen blithely saluting their long-time sponsor Carnation; Edward G. Robinson for Maxwell House, and Jimmy Durante sneezing for Scotties.

Groucho Marx opens the round window in the company logo again and says, with a salacious wiggle of his eyebrows, "Friends, go in and see your DeSoto Plymouth dealer tomorrow, and when you do, tell 'em Groucho sent you." Also unearthed is the prehistoric ad Marilyn Monroe did for an oil company, in which she refers to her car by the name Cynthia and coos to the attendants, "Put Royal Trident in Cynthia's little tummy."

Segments are linked with inane studio chit-chat from McMahon -- such a genial household figure now as to be beyond reproach, like the Pillsbury Doughboy or the Jolly Green Giant, both of whom he resembles -- and Mariette Hartley, who does a perfectly execrable job. But the commercials make the hour, and a stupendously satisfying hour it turns out to be.

By contrast, the fourth but unfortunately not last in the Dick Clark "Blooper" series tries to stretch about 12 minutes' worth of material into an hour, and feebly. Clark and a studio audience laugh so hard at such slender little gaffes (rescued from various cutting room floors over the years) that it's a wonder they didn't all have to be treated for hyperventilation every three or four minutes.

Clark is the host and producer, and the format accommodates plugs for NBC's "Taxi" ("the hit series," according to Clark) and "Fame" ("the hit series," according to Clark); both shows deserve to be hits, but at this point, neither is. William Shatner ambles by in extremely affable fashion to introduce or describe some of his movie fluffs, and there is a perfectly pointless appearance by that living absence of talent, Melanie Chartoff, of the justifiably dead "Fridays" show.

As before, the show's chief problem is that most funny bloopers are too dirty for TV. Still, two that involve blue language are included. The producers try to finesse this by manipulating the canned laughter so that the dirtiness does not seem to be what's getting the chuckles.

Last year's first outing of the try-out late-night "Twilight Theatre" series, coproduced by Steve Martin, gave every sign of also being the last. There was much Hollywood talk of production woes, and the show did not exactly send America into a fit of gratitude. But here it is, back again, shamelessly masquerading as the nation's favorite TV show, winner of 40 Styrofoam "Toynbee" awards, and hosted this time by the new reigning dead-pan king of the world, Leslie Nielsen, with begrudging assistance from Mr. T, of "Rocky III."

Roughly two dozen short skits are crammed into 90 minutes, some of them almost heavenly in their silliness -- be they a prankishly redubbed episode of the old "Commando Cody" serial (in the style of Firesign Theater's funny "J-Men" movie); a magician called The Great Tim (Fred Willard) who literally steals people's hearts; a '50s sitcom, "That Darn Kathy," in which the viewer gets to play the part of the ditzy heroine (Directions on the screen: "Get your head stuck in the fishbowl. Do it! Remember, you're an idiot"); Father Guido Sarducci (Don Novello) trying to drum up curbside confessions; and shocking proof from FDR's own lips that the Great Depression of the 1930s was all a hoax.

In a spirit of pure something, G. Gordon itself appears for a mock debate on national defense with Moon Unit Zappa in her Valley Girl mode. And Martin is seen guiding guests through the lavish recesses of his mobile home. As might be expected, some sketches -- like one in which under-budgeted actors must make their own sound effects -- wilt instantly, while others -- like a brief fantasy in which Big Foot comes out of the woods for a purpose no fouler than stealing women's clothing and prancing about in it on the lawn--seem possessed of adorable madness.

Others fall between funny and hilarious, some fall between ridiculous and absurd, a few waver between dumb and stupid, and still others could be said to shilly-shally between existential symbolism and filth. We shall count the hours until "Twilight Theatre" insists on appearing again.