OVER THE YEARS, we've seen plenty of once-funny sitcoms grow less amusing with age - the most recent being Frasier. But can an unfunny show evolve into a laugh getter? Three stinkers are attempting just such an unlikely feat by reworking themselves this season: Suddenly Susan (NBC, Mondays, 8-8:30 p.m.), Jesse (NBC, Thursdays, 8:30-9 p.m.), and Two Guys and a Girl (ABC, Wednesdays, 8-8:30 p.m.).
     One thing's for sure - they don't have history on their side. The only recent example of such a sidesplitting transformation is Ellen, which went from a mediocre Seinfeld clone to an uproarious groundbreaker with its coming-out episode. Its creative evolution lasted only half a eason, however, before Ellen DeGeneres' vehicle degenerated into acrimony, speechifying, and Ann Heche cameos. Now two Ellen vets, exec producers Mark Driscoll and Maria Semple, have taken on the Sisyphean task of saving Susan.
     Their best move was adding ex-Pythonite Eric Idle as Ian Maxtone-Graham, the Brit-twit editor who turns Brooke Shields' San Francisco city paper into a lad mag. Idle masterfully slips insults into proper-sounding sentences ("I look forward to a long and impersonal relationship with each and every one of you"). Along with returning players Nestor Carbonell (heavily accented hunk Luis) and Kathy Griffin (pesky pal Vicki), Idle gives Susan's banal lines a lift.
     Sadly, the same can't be said for the other new cast members - Currie Graham as a macho-dolt sportswriter and Melrose Place's Rob Estes as a free-spirit photographer. Nor can it be said for Shields. Ellen was salvageable because it centered on a gifted comedian; Susan is a lost cause because its star is stiffer than Al Gore.
     Jesse, on the other hand, has a limber lead in Christina Applegate. In its first season, however, it had little else aside from Bruno Campos as Diego, the on-again, off-again beau of Applegate's single mom. Campos is essentially playing the same part as Carbonell (the stud who talks funny), yet he and Applegate made a cute couple. Trouble is, that's not enough to sustain a series - especially one saddled with an otherwise weak supporting cast - and Jesse quickly turned stale.
     This season Jesse's buffoonish father and brothers are gone, and she's quit her barmaid job to study nursing. Her new coworkers include a snappish male nurse (the scene-stealing Darryl Theirse) and a squeamish doctor (Kevin Rahm). Too bad Jesse's scripts are still sickly. Suffice it to say that in the season premiere, the words butt crack figured prominently in no fewer than four punchlines.
     Which brings us to the sitcom formerly known as Two Guys, a Girl and a Pizza Place. The pizzeria where Berg (Ryan Reynolds), Pete (Richard Ruccolo), and Sharon (Traylor Howard) used to hang out no longer figures in the show, which producers promised would be more mature this fall. What they didn't seem to realize is that the new title is even more generic - and so is the series.
     Without the colorful restaurant denizens, all we're left with is monochromatic twentysomethings dealing with tired dating dilemmas. Pete pines for Sharon, but she's engaged to Johmy (Nathan Fillion). (Why two men would fight over such a detestably self-involved woman is never explained.) Berg bristles predictably when his new live-in lover, med-school classmate Ashley (Suzanne Cryer), redecorates his pad. Even without the pizza place, Two Guys remains the Domino's of sitcoms: The best thing about it is that it's done in 30 minutes.