A bad excuse even for a bad television show, "Tough Cookies," premiering at 8:30 tonight on Channel 9, stars whispery Robby Benson as a young Chicago police detective who's brash, eager and overpoweringly dumb.

The premiere of the new CBS comedy, which was written by Jan Fischer and William Weidner, is overstuffed with nuisance characters and burdened with a glum downer plot. Little Robby falls in love with a pert young TV news reporter (Gail Edwards) whom he meets at the scene of a murder. She gets mad when he doesn't phone one night and dumps him. And if that doesn't leave you laughing, maybe the jokes about gang warfare will.

Benson is all wrong for the role, and that's paying him a compliment; the show is a confusion of stale comedy ideas and drearily hedged bets.

Lainie Kazan, who can save almost anything, does bring some sparkle to the colorless role of a restaurateur, and one wonders why a series isn't developed for her. Alan Arkin's son Adam, biding his time as one of Benson's pals, gets to remark, "Sincerity is the key; if you can fake that, you got it made." Unfortunately, "Tough Cookies" can't, and doesn't.