TRANSAMERICA — ** — Felicity Huffman, Kevin Zegers, Fionnula Flanagan; rated R (profanity, vulgarity, drugs, nudity, brief sex, violence).

"TransAmerica" has a credibility problem. Not because of actress Felicity Huffman, who is convincing in the role of a preoperative, male-to-female transsexual.

This drama's problems have more to do with the script. It's full of enough contrived and ludicrous soap opera-type plotting to make Huffman's TV series, "Desperate Housewives," seem restrained and realistic.

Still, there's no denying that Huffman does give a terrific performance, one that has earned her an Academy Award nomination.

Huffman stars as Stanley Osbourne, or as he prefers to be known, Bree. Stanley has finally gotten approval to have sexual-reassignment surgery.

But there's one catch. He recently received a telephone call from Toby (Kevin Zegers), a teenage hustler who claims to be his long-lost son. So Stanley's therapist (Elizabeth Pena) is urging him to meet the boy and resolve any issues before having the surgery.

He winds up bailing Toby out of a teenage detention facility and takes him along on a trip to California. From there, the film basically turns into a road picture, with the two characters getting into a series of misadventures with a drifter (Grant Monohon), a kind-hearted American Indian (Graham Greene) and even Stanley's estranged family.

Screenwriter/director Duncan Tucker plays up some of the comic elements when he should be emphasizing the drama. And his plotting is so bizarre that at times it's quite off-putting.

However, he does get sterling work from Huffman, who nearly salvages the film all by herself. Unfortunately, she's paired with Zegers, who merely sulks. (And it's a shame to see Pena, Fionnula Flanagan and the always reliable Greene wasted in go-nowhere roles.)

"TransAmerica" is rated R for frequent use of strong profanity and other vulgar sexual talk, drug content (use of cocaine and hormone therapy), some full male and female nudity, brief simulated gay sex, and some brief violence (including fisticuffs). Running time: 102 minutes.