''According to one of my songs, I'm a charming and dangerous guy!'' says Robyn Hitchcock. So it shouldn't be a total surprise that the alt-rocker known for such gleefully loony '80s tunes as ''Balloon Man'' plays Laurent, a silver-haired ''British creep'' in ''The Manchurian Candidate.'' Director Jonathan Demme helmed Hitchcock's 1998 concert film ''Storefront Hitchcock'' and called him to audition. (Demme also cast R&B singer BeBe Winans as a government agent.) Hitchcock's open to more movie gigs, but says the parts are limited: ''Brits tend to be uncles, butlers, and villains,'' he says. ''We're either very wise and reassuring, or slightly gay. I don't know why.''