Melanie Chartoff could be the least talented person in all of network television; she even makes Suzanne Somers look good. Chartoff can't sing, can't dance, can't act (a "triple threat," to quote "Singin' in the Rain") and her timing is atrocious. Yet every week she is greeted with roars of approval by the urban yahoos who comprise the studio audience at "Fridays," ABC's fanatically low-rated rip-off of "Saturday Night Live."

Chartoff--who is rather pretty, in an Ornamental Ice sort of way--gets a roar again tonight at 10 on Channel 7 when ABC airs a special prime-time edition, which was designed to win new converts to the program but merely serves to confirm it as a plethora of shortcomings and a fest for amateurs. The semitopical, frequently physical comedy on "Fridays" is so shallow and undisciplined, you'd think you were watching a pack of cackling cutups from PS 84.

Assembling a group of stand-up comedians rarely results in group comedy. Some of the performers on "Fridays" do show spirited, nutty potential, but they are usually clobbered by barren or desperate material. The best sketches on "Fridays" are never half as good as the worst sketches on "SCTV Comedy Network."

Tonight, the only skit with much of a laugh factor is a brief parody of "Chariots of Fire" in which the three hero runners move in agonized slow motion while the rest of the competitors whiz by in real time. Cast member John Roarke has perfected a deft impersonation of Ronald Reagan, but that is seen only fleetingly tonight in a spoof ad for "Federalism Express."

Guest stars who drop by to no avail include the unsavory Tony Geary, William Shatner (who plugs his wretched ABC series "T.J. Hooker"), Marty Feldman and, disastrously, Paul McCartney and Stevie Wonder, in a mawkish dollop of promotional video supplied by Columbia Records to plug the pair's new release, "Ebony and Ivory." The gist of the song is, if black and white keys can live side by side on a piano keyboard, why can't black and white people live together in harmony, too? Heesh!

Actually that's not just the gist; that's the entire content. Paul McCartney (who is, before our very eyes, slowly turning into Fred Travelena, though Fred probably does a better McCartney impression) may deserve this kind of humiliation, but Stevie Wonder doesn't.

Much of the show's comedy depends on props, like Bruce Mahler's tired manipulation of butchered chickens. Rich Hall, who does have a knack for the whimsically offbeat, is very funny with his report from "Pitkinville," the Toonerville Trolley town, but he sticks out like a whole fistful of sore thumbs in the surroundings of this show.

Sometimes, as "SCTV" wends its way toward 1 a.m., one can sense the writers beginning to run out of ideas. With "Fridays," it's obvious they run out of ideas before they even get to the old drawing board. Surely six of the most dispiriting words in television are: " 'Fridays' will continue in a moment." The moment is never long enough.