John Travolta has so much star magnetism that he was able to give a delicate, winning performance even amid the gushy mystical banalities of Phenomenon; this time he goes down with the ooze. As Michael, an archangel with big white-feather wings and an even bigger attitude, Travolta gets to play a saint and act mildly sinful at the same time. How incorrigible is Michael? Well, he smokes, he drinks, he wears his hair like Vinnie Barbarino; he tells bad jokes like ''What's the opposite of white? Yolk!'' As Michael drives to Chicago with a trio of tabloid reporters who've been sent to Iowa to do a story on him, the director, Nora Ephron, displays her peerless gift for making everything seem snappy and mushy at the same time. Travolta's performance has a slovenly, I-can-do-anything-and-you'll-still-love-me obnoxiousness. When he performs a wild and crazy dance to ''Chain of Fools'' along with a barroom full of women who adore him (because, according to the film, he smells like cookies), it's the first Travolta dance scene that makes you want to look away in embarrassment. (All that's missing is a lampshade on his head.) Still, even that's preferable to watching him get transformed, a la Phenomenon, into another celestial healer. Two Messiah figures in one year is at least one too many for any actor. Seen in the light of his proselytizing embrace of Scientology, these heavenly-savior roles are starting to make Travolta look like a walking mission statement. Michael eventually becomes a rerun of Ephron's Sleepless in Seattle, with William Hurt and Andie MacDowell, in the sleepiest romance of the season, gingerly drawn together by Travolta's magic. If only we could feel it too.