WHEN staging a classic play, Ingmar Bergman doesn't always take a classic approach. When his thrilling avant-garde production of "Hamlet" played at the Brooklyn Academy of Music (BAM) a few seasons ago, it infused the venerable drama with layers of new visual and dramatic meaning.There was less revisionism in the recent "Bergman on Stage," a series of three Bergman productions at BAM that were part of the New York International Festival of the Arts, courtesy of the Royal Dramatic Theatre of Sweden. The plays themselves were certified major works by key playwrights: Strindberg's psychological study "Miss Julie," O'Neill's intense family drama "Long Day's Journey Into Night," and Ibsen's prophetically feminist "A Doll's House." Mr. Bergman treated each one in a fairly traditional w ay, emphasizing character development and subtleties of performance rather than visual or thematic innovation. Yet a trend toward decreasing realism and increasing stylization was clearly detectable as the series unfolded, especially in the staging Bergman chose for each drama. The action of "Miss Julie" included some elements that were not strictly naturalistic, yet everything was confined within the walls of a realistically detailed set. By contrast, "Long Day's Journey Into Night" took place on a raised platform that seemed almost to hover in time and space, a device that brought out the universality of the play and its tormented characters. "A Doll's House" carried this even farther, with characters remaining fully visible during their offstage moments, sitting on both side s of the platform that represented the home of Nora and her family - a brilliant idea on Bergman's part, since it illustrated the influences and connections that tie Ibsen's characters together. The other distinguishing characteristic of the Bergman series was its excellent performances, especially by such Bergman regulars as Peter Stormare (Jean in "Miss Julie," Edmund in "Long Day's Journey"), Erland Josephson (Doctor Rank in "A Doll's House"), and Bibi Andersson, whose Mary Tyrone dominated the O'Neill play with extraordinary authority. Pernilla Ostergren's robust Nora also lent uncommon dramatic energy to "A Doll's House." BAM has been keeping a busy schedule quite apart from its participation in the international arts festival, and one recent event was particularly newsworthy: "Hydrogen Jukebox," a rare collaboration by two prodigious talents, "beat" poet Allen Ginsberg and "minimalist" composer Philip Glass. The evening offered an eccentric guided tour of the American landscape - mental and physical - through 21 poems set to music. Although it was well played by a six-person ensemble, Mr. Glass's score rarely gathered the momentum and drive that has characterized his best work (the masterful "Einstein on the Beach," for example), and Mr. Ginsberg's poetry gained nothing from the musical settings or from the mostly unintelligible singing of six onstage performers; the best moment came when the poet simply rea d his classic "Wichita Vortex Sutra." Jerome Sirlin, who staged Glass's more memorable "1000 Airplanes on the Roof" a few seasons ago, did the uninspired production design. In all, the evening was a disappointment for the eye, the ear, and the mind.