At Magazines, the Art of Stirring Debate Seems Lost
American magazines no longer drive public debate, and editors and writers offer several reasons; Norman Mailer, whose article on Pentagon took up entire March 1968 issue of Harper's, claims magazines today are driven by ads; David Halberstam, who writes for Vanity Fair, says most magazines have become diminished in seriousness, with celebrity journalists interviewing Hollywood personalities; most glaring reason is there are fewer general-interest magazines that unify broad national audience; most new magazines that come into marketplace are niche publications; Neal Gabler, cultural historian and author, claims magaziness are no longer writer-generated, they are subject-generated; photos (M)

