Once upon a time, there were twin sisters. One was smart and plain, with brown hair. The other was dumb and girlie -- oh yes, and blond, very blond. Together, they traded catty insults while a robotic audience cackled with glee.
''Twins," which premieres tonight at 8:30 on Channel 56, is a painfully simplistic sitcom that has exactly one thing going for it: Sara Gilbert. The former ''Roseanne" star may own the most relentless deadpan in TV history, a stiff mask through which you can always read her true -- and usually contemptuous -- feelings. She brings enormous dimension to expressionlessness, and if I ever watch this show again, which is unlikely, it will be to enjoy the range of her poker face.
Gilbert plays Mitchee, who runs her parents' lingerie company with her sister, Farrah (Molly Stanton). Yes, the blond ditz is named Farrah, which offers a hint of the show's proud obviousness. While Mitchee is the brains of the operation, Farrah is the face -- or rather, the body, since she models the products, including a new underwear called ''The Buttpucker." Tonight, she spends a fair amount of time working, which means she flaunts a lot of skin, which means the WB isn't disappointed that the series is set in the world of panties and bras. Farrah is indeed ''High School Dropout Barbie," as Mitchee calls her, and we can probably expect the writers to give her a College Frat Boy Ken before too long.
Produced by the makers of ''Will & Grace," ''Twins" also heralds the TV comeback of Melanie Griffith. She's the second stupe, competing with Farrah for the Most Clueless in Show prize. Which one is dumb, and which one is dumber? It's a close race. As the mother of the twins, Griffith delivers her moronic lines with an oddly listless rhythm, emphasizing the biggest problem with ''Twins": that too much thickness can quickly wear thin.
Matthew Gilbert can be reached at firstname.lastname@example.org.