I HAVE SOME problems with "The Sisterhood of the Traveling Pants," but let's start with the pants.

As in the best-selling book by Ann Brashares, on which this film is based, the titular trousers are a pair of jeans that, against the laws of nature, manage not just to fit but to flatter the derrieres of four very differently proportioned teenage girlfriends, each of whom thereupon agrees to rotate ownership of said slacks as the quartet embarks on a summer of life-changing adventures.

Now what might work in a novel, where we can imagine, but don't have to actually see, four rear ends of various shapes and sizes squeezing into what we are meant to believe is a single pair of denims, emphatically does not pass muster on film. We watch Carmen (America Ferrera, whose Rubenesque figure is matched only by her outsize talent) appearing to don, with only the slightest difficulty, the same pair of jeans that recently hugged the flesh of her friend Tibby (Amber Tamblyn, a waif-like slip of a girl whose tush seems to occupy negative space). The pants also fit the athletic thighs of Bridget (Blake Lively) and the more sedentary lower half of artist Lena (Alexis Bledel).

Must be "some kind of Lycra" in them, speculates one of the teens. (Would you believe pixie dust?) "It's scientifically impossible!" marvels another.

Ah, yes. Scientifically, but not cinematically. You see, we are now entering a world where anything is possible, including friendships among four people who appear to have virtually nothing in common, besides being works of fiction. Which brings me to my second, and bigger, problem. Like the women on "Sex and the City" -- or the members of the Spice Girls for that matter -- the central characters of "Sisterhood" are fantasy archetypes rather than living, breathing human beings.

There's the emotionally volatile, half-Puerto Rican Carmen, who narrates the film, and whose visit to her divorced gringo father (Bradley Whitford) and his blond wife-to-be (Nancy Travis) precipitates an identity crisis; sporty, sexy soccer star Bridget, whose grief over her mother's suicide pushes her toward dangerously inappropriate sexual behavior; shy, artsy Lena, who defies her Greek grandparents to date a hunky college boy (Michael Rady) while vacationing on Santorini Island; and the suburban-punky-would-be-documentary-filmmaker Tibby, whose "I hate the world" attitude softens after meeting a preternaturally wise but doomed neighbor (Jenna Boyd).

I just don't buy it. Sure, many friends are nothing alike. But while each individual perfomance is convincing, I never felt, or believed, the connection among these four.

Part of that is the fact that, as a grown man, I'm not exactly in the market for magical stories about girl bonding. But I also think this movie, as brought to life by director Ken Kwapis, who's better known for his television work, and screenwriters Delia Ephron and Elizabeth Chandler, does a particularly poor job of selling its own artificial reality. It feels like a metaphor that's still stuck on the page. The girls in "Traveling Pants" are only mannequins wearing someone else's clothes. They don't get inside your head, let alone your heart.

THE SISTERHOOD OF THE TRAVELING PANTS (PG, 120 minutes) -- Contains thematic material related to teen sexuality and the death of loved ones. Area theaters.

America Ferrera, left, and Amber Tamblyn as unlikely friends in "The Sisterhood of the Traveling Pants."