Director Hugh Wilson's romantic comedy Blast From the Past is as pleasantly plastic as its retro-chic sets. Coasting on his air of genial imbecility, Fraser plays a 35-year-old named Adam who's led a sheltered life -- bomb sheltered, that is. He was raised in a bunker after his mad-scientist father (Christopher Walken, of course) mistook a plane crash for a missile hit in 1962. Silverstone plays Eve, the tough cookie who -- in an inversion of ''Pleasantville'''s time-tripping gags -- wises him up to the ways of this uncouth decade upon his ascent to contemporary Los Angeles. Will Adam and Eve find true love? Is there swing music on the soundtrack? Duh and duh.