GODS AND DUDS: Review

''[DIVO]'' stands as a kind of handbook for the singer - with cautionary wisdom and practical advice for the novitiate, but also offering the operatic outsider a look at the vocal art as it takes shape within the singer's body. ''Skeletons From the Opera Closet'' is thinner in every way - appropriate, perhaps, for short subway rides to and from Lincoln Center. ''Diva,'' as the dictionary tells us, translates as ''opera singer,'' ''star,'' also ''goddess.'' ''Divo,'' then, is its male equivalent; and in her book of the same name, Helena Matheopoulos, the author of ''Maestro: Encounters With Conductors of Today,'' spends most of her time wisely standing aside and allowing the world's pre-eminent tenors, baritones and basses to tell us how they cope with that most mysterious of musical instruments - the human voice.