Just because you're a household name doesn't mean you're guaranteed a spot on TV's fall schedule. Ask Jessica Simpson, Chris O'Donnell, Gina Gershon, and a host of other actors who saw their TV careers slip away when the networks announced their new lineups earlier this month. The most significant rejection slip may have gone to Ms. Stinky Ass herself, whose ABC comedy had her touted as the next Kelly Ripa. But the net's brass nixed Simpson's turn as a ditzy TV reporter. ''It wasn't the best vehicle for her,'' admits ABC entertainment president Stephen McPherson. ''So we're gonna do a bunch of specials with her instead. She can sing and really be a star.'' No such consolation prizes for Gina Gershon, whose ABC comedy (costarring Simpson's husband, Nick Lachey) failed to make the cut. Her portrayal of a hot single mom was ''just not funny,'' says a producer on the pilot. The same could be said for the NBC comedy ''Everyday Life,'' starring Rob Reiner and Mercedes Ruehl, and CBS' ''The Amazing Westerbergs'' with Chris O'Donnell (''He wasn't funny enough to center a show around,'' says a net insider). ''Just because a star's attached doesn't necessarily mean it's going to get picked up. If it's no good, it's no good,'' says United Talent Agency partner Martin Lesak. ''At the same time, if a star has any judgment at all, he shouldn't want his show picked up if it's bad.''