With his surprisingly tart and nervy performance in Fox's new drama “Head Cases,” debuting tonight at 9 p.m., Chris O’Donnell could be the next never-quite-a-movie-star to find a large, devoted audience by moving to a TV series.
   The glamour in show business usually is in the other route, going from a TV series to movies. It’s looked upon as moving up. That’s the route taken by “E.R.’s” George Clooney, “Welcome Back, Kotter’s” John Travolta and, way back, “Rawhide’s” Clint Eastwood. They’ve become not just movie superstars, but icons.
   Yet there’s much to be said for the reverse path for talented actors who, whether because they get typecast early or just plain lack enough big-screen charisma to be the next Tom Cruise or Julia Roberts, look to television series for a breakthrough.
   Kyra Sedgwick certainly found it this summer in “The Closer.” Before that, Kiefer Sutherland in “24” and Sarah Jessica Parker in “Sex and the City” are notable examples. (As a teen, Parker starred in a TV series, “Square Pegs.”) In all these cases, they were able on television to slowly create empathy for their multifaceted, fascinating characters in ways that two-hour movies didn’t allow them. And by doing so they reinvented themselves.
   Now O’Donnell bids to follow suit. He is immensely appealing in “Head Cases” as driven, yuppie corporate attorney Jason Payne who, following institutionalization after a nervous breakdown, becomes a scrappy champion of the underdog. He also pairs up with a slovenly attorney who also was institutionalized and still seems borderline crazy. They are both law partners and outpatients of the same crusty therapist (Rockmond Dunbar).
   A well-written, offbeat actors’ showcase created by “The Practice’s” Bill Chais, “Head Cases” lets O’Donnell stretch and show off the depth of his performing skills.
   Cast in “Scent of a Woman” and several “Batman” movies as a sweet and innocent guy, the handsome O’Donnell here gets to burrow into that safe image with flashes of wit, nervousness and anger. He also reveals a screwball-comic flair that--when teamed with co-star Adam Goldberg as his quarrelsome law partner--recalls “The Odd Couple” or “Moonlighting.”
   O’Donnell has a natural partner/adversary in Goldberg’s neurotic Shultz, a reverse-“Monk” type whose anger disorder causes him to lose control and yell at judges, beat other attorneys with their law books, and just plain act like he needs a straight jacket rather than a coat and tie. His only clients are hookers and nymphomaniacs.
   Goldberg, who also makes independent movies and seems to relish the aesthetic of edginess, constantly flirts with the violent part of his character’s dark side. He’s both funny and ready to explode.
   One of the first episode’s best scenes comes early and serves as a harbinger for “Head Cases’” tricky, ever-shifting tone. Jason has a breakdown while watching a television newscast about his legal victory. Suddenly the newscast starts speaking directly to him. “I can control this,” a suddenly worried Jason says. But he can’t and eventually collapses as the hallucination grows more intense.
   As the hour progresses, “Head Cases” has more tonal shifts in store. There is slapstick, whenever Shultz picks a fight or kidnaps a witness. There’s sophisticated verbal humor. There’s sentimentality when Jason tries to see his estranged wife and son. There’s realistic courtroom drama. And there’s sincere exploration of mental disorders. There’s always potential for tragedy but also lots of laughs and engrossing drama.