On screen, British popster David Bowie has been cast as the epicene outsider (think of The Man Who Fell to Earth, his Pontius Pilate in The Last Temptation of Christ). Who'd have guessed that all along he just wanted to play a regular guy? When Bowie heard about producer Arnold Orgolini's latest project, a new romantic comedy, The Linguini Incident, he wanted to play Monte, a bartender with an eye for the ladies. ''The part was designed for someone in their early 30s, and Bowie is in his 40s,'' says Orgolini. ''But when we met, he looked like he was 22.'' Though Bowie plays it straight, the movie, which just finished shooting in New York, doesn't suffer from a shortage of eccentrics. Joining him are Rosanna Arquette as a waitress with a Houdini fetish and Eszter Balint as a trashy-lingerie designer.