SERIES DEBUT

WHAT: "Monk"

WHEN: 9 p.m. Friday

WHERE: USA Network

GRADE: B

"The defective detective."That's how one police officer scornfully describes the obsessive-compulsive homicide investigator played by Tony Shalhoub in "Monk," a witty and whimsical new drama series on the USA Network.Adrian Monk, we learn in Friday's two-hour pilot, is actually quite a gifted gumshoe. But he also happens to be afflicted with an array of tics and phobias that create an incredible challenge to dealing with sleuthing, not to mention everyday life.Monk has developed an abnormal fear of germs, heights, street traffic, crowds and even milk, for crying out loud. The disorders were triggered by the mysterious -- and still unsolved -- murder of his wife four years ago and became so debilitating that he was discharged from the San Francisco police force, despite the fact he possesses remarkable mental powers.Now, aided by his nurse and sidekick, Sharona Fleming (Bitty Schram), he is attempting to get back in the crime-fighting game. The opener has Monk helping the cops track down a sniper who sprayed gunfire upon the Financial District during a campaign speech by a popular mayoral candidate. The shooter also just might be responsible for the separate murder of a young woman.The story, penned by executive producer Andy Breckman ("Rat Race") gets predictable at times, but it deftly manages to mix drama and humor while bringing new twists to a shop-worn genre. And it's a real hoot to watch the eccentric, fidgety Monk dissect a crime scene while simultaneously grappling with his many neuroses. Winningly played by Shalhoub ("Wings," "Men in Black II"), our hero is part Sherlock Holmes, part Inspector Clouseau and part Rain Man.An added bonus is the presence of the charming Schram. We haven't seen much of her since she starred opposite Geena Davis in "A League of Their Own," and that's a shame. As Monk's "Girl Friday," she's a grounding presence and brings an engaging bit of sweet-natured chemistry to their relationship.In recent years, USA has had a pretty lousy track record when it comes to establishing signature series, but, at least upon first glance, "Monk" looks like a keeper.