Friday nights are light on inspiration Except for 'Legacy,' networks surrender day to kids and cliches.

One of the least-watched nights of television is also the least inspiring of the new fall season. ABC is adding a couple of new shows to its teen-oriented "TGIF" lineup, while NBC tries a conventional drama from a noted producer. The best of the new batch won't be out for three weeks. Pick to click "Legacy," coming Oct. 9 on UPN (Channel 29), is a new period drama from Chris Abbott, the "Dr. Quinn, Medicine Woman" producer and one of the few women allowed to run a TV show (Martha Williamson of "Touched by an Angel" and "Promised Land" is another). The story of an Irish family occupying a rich Kentucky plantation shortly after the Civil War, "Legacy" is super-wholesome and beautifully filmed, with a nice Celtic soundtrack. It may well be the successor to "Dr. Quinn," provided viewers can find it on the dial. What else is new "Trinity," debuting Oct. 16 on NBC, is worth a look, if only because "ER" executive producer John Wells is behind it. It's also the story of an Irish family, this one having grown up in New York City's tough Hell's Kitchen neighborhood, where Mom and Pop still live and where the 20- and 30-something siblings still convene every week for Sunday dinner. The show, unfortunately, is mapped out like a sitcom - one brother is a cop, another is a union organizer, a third is a priest - and that just won't cut it on Friday nights, when viewers must be enticed to watch TV. Of course, when you think family and Friday-night TV, you think of ABC's long-running franchise of teen-oriented sitcoms. Two new entries join the "TGIF" stable this fall. "Two of a Kind" brings America's darling duo, Ashley and Mary-Kate Olsen, back to the small screen. After sharing the part of Michelle on the old ABC hit "Full House," the twins share a stage in a show that has "kiddie sensation" written all over it. It debuts at 7 tonight on Channel 9. Mary-Kate is the tomboy, so look for her in hats and pants. Their dad (Christopher Sieber), who naturally is a widower, teaches at the local college, where one of his students (Sally Wheeler) answers the classified ad for the girls' babysitter. At 8:30 p.m. on Channel 9, "Brother's Keeper" offers William Ragsdale (Herman in "Herman's Head") as a professor who's assigned to watch over his younger brother, Bobby (Sean O'Bryan), as part of Bobby's pro football contract. With its slightly more mature premise, it isn't exactly the next "Sister Sister." With the hiring of Justin Cooper, last seen in "Liar Liar," "Brother's Keeper" starts TV's oddest trend; that of hiring cute kids from blockbuster Hollywood films to make Friday-night sitcoms. Last year, Jonathan Lipnicki of "Jerry Maguire" starred in the stinky "Meego." "Buddy Faro" (8 p.m. on Channel 5) is the second of two new Rip Van Winkle detective shows ("Brimstone" on Fox is the other). Dennis Farina plays a famed Los Angeles sleuth who vanishes one day in 1978 before being smoked out by another P.I. (Frank Whaley). This Aaron Spelling-produced action comedy is supposed to evoke the Rat Pack era, but I wasn't especially taken by its attempts at camp, and I've had it with car chases, even the cutesy chase in tonight's episode involving Buddy and two Abe Vigoda types. Amazingly, as of this writing "Living in Captivity," the horrible sitcom from "Murphy Brown" creator Diane English about a black couple moving to the all-white suburbs, is still on the air (7 p.m. on Channel 4). Surfin' turf Fox's horror drama "Millennium" gets a makeover this fall when Frank Black (Lance Henriksen) moves from Seattle to Washington and goes to work for the FBI, where he is paired with a lovely, if unapproachable, agent (Klea Scott, last seen on "Brooklyn South"). The show's executive producer, Chris Carter, says these changes are part of an overall plan to make "Millennium" more "hopeful." And if the result is a show that looks more like Carter's smash hit "The X-Files," all the better.