NOW THAT NO one takes Crosby Stills Nash seriously anymore, one can appreciate them as the pleasant lightweights they are -- the Four Seasons of the '70s, as it were.

Like the Four Seasons, Crosby Stills Nash (they've dropped the "&") can sing prettily and their earnest sentimentality summons up a particular era quite readily. And just as the Philadelphia quartet once tried to keep up with the times with "The Four Seasons Sing Big Hits by Burt Bacharach/ Hal David/Bob Dylan" (recently reissued by Rhino), so has the California trio released a comeback album, "Live It Up," that is torn between awkward attempts to be modern and familiar imitations of their old sound.

Even when they try to be up-to-date, CSN seem a step behind the times. "Live It Up," the title track and first single from the album, is a synth-driven dance-rock number that was already dated when it was first recorded in 1986. The Sting-like combination of programmed worldbeat rhythms, Branford Marsalis soprano sax and bleeding-heart politics never quite gels on "Yours and Mine." Much better are the fluffy midtempo pop songs, where the trio's feathery harmonies can still work their magic.

The first single should have been either Stills and Nash's "(Got to Keep) Open" (with Bruce Hornsby on accordion) or the J. D. Souther/Danny Kortchmar number "If Anybody Had a Heart."