Partly a biography of ""the most influential media baron of our time,"" more a critique of that baron's stewardship of the public interest, an ambitious assemblage that falls short of a strong narrative or full indictment. Newsday reporter Maier never received access to his little-known subject -- S.I. ""Si"" Newhouse Jr., ruler of a chain of newspapers, of CondÃ‰ Nast Publications (publisher of Vogue and Vanity Fair, among other magazines), and of the Random House book publishing empire -- so his portrait is understandably sketchy. After tracing Newhouse's youthful unhappiness and professional meanderings, the author gets sidetracked with more interesting characters, such as Si's ""surrogate father,"" Alexander Liberman, longtime editorial director of CondÃ‰ Nast. There, Newhouse blurred ""the distinction between editorial and advertising,"" Maier writes, sins later magnified at the reborn Vanity Fair and the newly acquired New Yorker. The narrative then turns to Si's friendship with the notorious Roy Cohn, who set in motion what seems to be Newhouse's most glaring ethical lapse: the Newhouse-owned Cleveland Plain Dealer succumbed to Mafia pressure to retract an investigative story on Teamster boss Jackie Presser. (Like most controversies in the book, this has been reported on in depth before.) Maier moves on to the complex tax maneuvering that saved oodles for Newhouse's Advance Publications, allowing him to acquire Random House in 1980. The author recounts how Newhouse's bottom-line mentality led to the controversial firings of veteran editors and sullied the company's reputation. Profiling editor Tina Brown (who agreed to interviews), he reveals that Si had planned to pull the plug on Brown's Vanity Fair until the famous Reagan cover turned the magazine's fortunes around. Si often drops out of the narrative when it veers into lengthy but not probing reports on the personalities and internal politics of Newhouse's empire, but Maier makes the worthy point that pundits have rarely examined the way ""the nation's largest private media company"" affects journalism and culture. In the public interest, surely. But will the public, outside the media world, be interested in this mediocre effort?