It's a measure of the star power of Julia Roberts that she dominates the threadbare romantic comedy "The Very Thought of You" without actually appearing in the movie or even being mentioned in the screenplay. That's because Monica Potter, playing a brash young woman from Minneapolis who flies to London with $35 in her pocket to start a new life, has been directed to "be" Ms. Roberts in spirit, if not in body.

Insofar as one actor can impersonate another without doing an out-and-out caricature, Ms. Potter offers a reasonable facsimile of Ms. Roberts' all-American princess with her mercurial blend of pluck, pliability, defiance and sweetness. "The Very Thought of You," directed by Nick Hamm from a screenplay by Peter Morgan, is one of those coyly edited movies that fills in the mystifying gaps in its story by periodically doubling back to repeat a scene with new crucial information added. In its opening moments Laurence (Joseph Fiennes), the movie's frantic narrator, bangs on the door of a neighbor (Ray Winstone), whom he thinks is a psychiatrist, at 4:30 in the morning and pleads for an emergency therapy session. The whys and wherefores only become clear very late in the game. To maintain its fizz, a comedy like "The Very Thought of You" requires the spicy contemporary equivalent of Noel Coward banter. But if the story is a clever sitcomy contraption, the dialogue is pedestrian. Among the contestants for Martha's love, the only character with a distinctive personality is Hollander's vain, petulant Daniel, whose ego is in need of puncturing. As the shy, tongue-tied Laurence, who needs lessons in self-assertion, Fiennes lacks the debonair twinkle and the comic timing of Hugh Grant, who might have made the role come alive.

As for Ms. Potter's Martha, the character is a fabrication that not even Ms. Roberts with all her wiles could have made believable. Given a paucity of clever dialogue, she verges on being an irritating. self-centered nag, not the all-American princess who deserves the "happily ever after" ending signaled from the moment she first appears on the screen.

PRODUCTION NOTES

Rating: "The Very Thought of You" is rated PG-13 (Parents strongly cautioned). It includes some racy dialogue and sexual situations.

Directed by Nick Hamm; written by Peter Morgan; director of photography, David Johnson; edited by Michael Bradsell; music by Ed Shearmur; production designer, Max Gottlieb; produced by Grainne Marmion; released by Miramax Films. Running time: 88 minutes. This film is rated PG-13.

Cast: Monica Potter (Martha), Rufus Sewell (Frank), Tom Hollander (Daniel), Joseph Fiennes (Laurence) and Ray Winstone (Pedersen).