“Legally Blonde” is criminally stupid. The basic storyline, about a ditzy California sorority gal who gets into Harvard Law School to pursue the long-time college beau who’s dumped her for the crassest of reasons–only to stumble her way to professional success and true romance in the process–could make for a funny, maybe even heartwarming film: after all, the same basic not-so- dumb blonde shtick has worked in pictures ranging from “Born Yesterday” to “Working Girl” to “Clueless” (not to mention many of Marilyn’s movies). But here everything is so forced and italicized that the result has all the charm of fingernails scraping a blackboard for ninety minutes.

The central difficulty is that the script is half campy cartoon and half sniffling schmaltz, with very little in between. Heroine Elle Woods (Reese Witherspoon) is first depicted as a slightly spacey, self-centered, materially-oriented thing, but whenever the plot finds it convenient, she suddenly becomes bright, highly principled, and extraordinarily generous. By the close–a wish-fulfillment courtroom victory that’s completely idiotic (and features a truly execrable homophobic aside)–she’s still dressing like a Beverly Hills brat and carrying around her oh-so- cute, pampered pooch everywhere she goes (the mutt is employed in so many inserts that it’s akin to both animal and audience abuse). But she’s also acted as matchmaker for an unhappy middle-aged manicurist, become a virtual role model for her ex’s initially snooty new squeeze, caught the eye of a sweet-natured attorney, and secured the acquittal of a sorority sister wrongfully accused of murdering her much older husband. Comedy needn’t be a mirror of life, of course, but it needs some grounding in reality. “Legally Blonde” has absolutely none.

The weakness of the script is compounded by the presence of Witherspoon in the lead; she’s simply miscast as the loopy protagonist. The young actress radiates intelligence–a quality she has joined with brusque obsessiveness in “Election” and naive vulnerability in “Cruel Intentions”–but as a brainless ninny she’s about as convincing as (to use a reverse analogy) Angelina Jolie might be playing a rocket scientist. Witherspoon is simply too good an actress to be doing the equivalent of a bad SNL skit for an agonizing hour and a half. None of the other performers make much of an impression, either. Luke Wilson is so laid-back and unobtrusive as Elle’s Mr. Right that he almost disappears from the screen, while Matthew Davis comes off so smarmy and callous as her Mr. Wrong that we know from his very first scene what the dismally obligatory “what happened to” caption added to the inevitable still-frame at the end will say about him. Victor Garber’s performance as a singularly inept fellow who’s said to be the best defense attorney in Boston (Bobby Donnell should sue for misrepresentation) proves that he’d best stick to the Broadway stage, where his talents are employed to greater effect. And there’s a really embarrassing turn by Raquel Welch as the murdered hubby’s bitchy ex-wife. One could go on indefinitely about the weaknesses of individual cast members, but they’re really not to blame. It’s impossible for any actor to fill in a role that’s no more than an empty hole in a script’s shooting pages, and here the screenplay is the equivalent of Swiss Cheese in that regard. Robert Luketic’s flat, meandering direction doesn’t help matters; instead of trying to conceal the flaws, he actually highlights them.

Where’s John Houseman now that we really need him? If only Professor Kingsfield had been around to shroud Elle Woods on the first day of classes, she might have disappeared at once and the wretched remainder of “Legally Blonde” gone with her. Unfortunately, the teaching staff at Harvard Law seems to have deteriorated markedly, at least on screen, since the days of “The Paper Chase,” and having a movie this bad use the institution’s name at all is a sign of continuing decline. (Surely someone in authority in Cambridge should have objected to a truly insulting scene showing how Elle gets the thumbs-up from the admissions committee.) This is one picture that would deserve to be banned in Boston–and everywhere else–not on grounds of immorality, but of simple incompetence.