Inspector Gadget demonstrates how a movie with little more on its mind than tickling the eyeballs of 7-year-olds can feature spiffy, jack-in-the-box special effects and still end up a dud. Based on a cartoon series, this latest attempt to launch a Disney kiddie franchise stars Matthew Broderick as Inspector Gadget, a half-human, half-android crime fighter who issues a trademark command of ''Go, go, gadget ... magnifying glass!'' (or whatever it is he needs) to convert his limbs, digits, and trusty fedora into every imaginable gizmoid contraption. His thumb opens into a cigarette lighter, his fingers sport a skeleton key and bubble wand, and helicopter blades whirl right out of his hat. He's like a pop-up-book fusion of Edward Scissorhands, RoboCop, and a Swiss Army knife.
The trouble is, each feat of animatronic wizardry lasts for about five seconds. (You only wish that Rupert Everett's mincingly grotesque performance as the villain lasted that long.) Chasing down some bad guys, Gadget will sprout, say, a pair of spring-wired stilt legs, and the movie then cuts to a boring close-up of Matthew Broderick's face as he's ''running.'' The entire image of this kitchen-magician dream robot comes at us in little jolts and spasms that have the zappy, self-contained rhythm of a fast-food tie-in commercial.
In a Disney romp like Flubber, goofy and dumb as it was, Robin Williams, who's practically a special effect himself, knew how to dance and joke around his ricocheting Jell-O costar. Broderick, on the other hand, simply looks flabbergasted. He does finally lighten up a bit as Gadget's evil twin, a ''bad'' robot whose nightmare choppers make him resemble one of those rubber Richard Nixon masks. His gadgets, including some major machine guns, go by with similar perfunctory flash, but Broderick, at least, looks like he's getting a kick out of them. C-