If only Jim Carrey's uninhibited and completely unhinged, sweet-and-sour insanity was by itself enough to carry a movie, it might not matter so much that the plot of the Farrelly Brothers' "Me, Myself and Irene" is nothing but an undercooked on-the-run road movie.

Full of crooked cops and rich, double-crossing ex-boyfriends, it's a dim bulb script the boys had shelved ages ago and dusted off last year only after a couple post-"There's Something About Mary" projects fell through.

Sustained only by its outrageousness (breast milk gags, anyone?) and Carrey's hammy physical humor, the movie does have its fair share of laughs. But between guffaws there's nothing to keep the uneven "Irene" from collapsing under its own dead weight.

For the most part, Carrey is a riot as a milquetoast Rhode Island state trooper named Charlie Bailygates, whose bottled aggression has turned him into a schizophrenic pressure cooker. Everyone in his seaside town pushes him around -- even a little girl he warns against jumping rope in the street. But when he's not medicated, out pops Hank, Charlie's suppressed and vengeful Id personified as a vulgar, bellicose, sex-mad maniac.

Assigned to transport a comely prisoner named Irene (Renée Zellweger) to New York where there's a warrant for her arrest, Charlie fall in love with the girl instead and goes on the lam with her after she explains she's been framed by her sinister, country-club beau (Daniel Green, "Kingpin") for some corporate crime so random and irrelevant that I can't even remember what it is. Of course Hank -- who after a while pops up for no logical reason whenever the script needs to be buttressed -- has the hots for Irene as well, and he's all paws and sexual innuendo whenever she's within reach.

Carrey's incredibly pliant face goes through wild rubbery permutations as he passes between his two personas, and the Farrelly's let him completely off his leash as Hank -- which doesn't always work to the movie's advantage.

But he once again proves he's a better actor than Hollywood gives him credit for when toward the end of the picture Hank and Charlie start seeping into each other's personalities. The gradual melding is the only subtle thing in the whole movie, and Carrey brings it off without losing sight of the screwball nature of either part.

Unfortunately, directors Peter and Bobby Farrelly (who wrote the film with boyhood friend Mike Cerrone) don't have the same kind of grasp on the story that Carrey has on his characters. The picture jumps helter-skelter between sketch comedy set pieces without any sense of flow as Charlie, Irene and sometimes Hank run from the boyfriend and the bad cops (Chris Cooper and Richard Jenkins) on his payroll.

Inevitably, "Me, Myself and Irene" sets up a slapstick battle for the body between Charlie and Hank, giving Carrey his chance to one-up Steve Martin's internal skirmish rag doll routine from "All Of Me." The bit gets old in a big hurry.

The funniest performances in this movie aren't from Jim Carrey at all, in fact. They're from Anthony Anderson ("Big Momma's House"), Mongo Brownlee ("Bulworth") and Jerod Mixon (also in "Bulworth") as Charlie's three ghetto-smack-talking, super-genius black sons.

See, the movie opens with a prologue from eighteen years ago, when Charlie's new bride (Traylor Howard) ran off with the midget, Mensa-member, African-American limo driver (Tony Cox) that took them home from their wedding. She got knocked up, gave birth to triplets and left Charlie to raise them.

The Farrelly's dialogue for these guys is a hilarious mix of street slang and book smarts ("Wit' a 1430 on you SATs, you lucky if you get into Duke, fool!"), and every time they show up to steal a scene it's a reminder how stale the rest of the movie seems.