Art is anything you can get away with,"" says Marshall McLuhan who clearly gets away with a great deal which is neither art nor cricket. He comes on like the fourth law of thermodynamics sputtering through the fifth dimension. ""I am in the position of Louis Pasteur,"" he announces, preparing to usher us into ""the cool millennium."" His laboratory is the ""electric age,"" bubbling with sensory stimuli, programmed actions, centralized computer systems, and Gregorian invocations to ""a general cosmic consciousness."" Technology has changed our world and our psyches, says Professor McLuhan: the linear mode of discourse or dramatization is obsolete; we are on the threshold of a visual and auditory breakthrough: day by day a universal code, a universal language assume their blessed shape, ""a Pentecostal condition,"" the electronic realization of man's dream. Thus, ""the medium is the message, or in a hippier term, ""the massage"" No, McLuhan is not talking about TV or Telstar; he is talking about Big Brother, ""live"" and benevolent and au courant. Naturally, McLuhan is the Man of the Moment, and in the anthology here a number of our best brains (Father Ong, Frank Kermode, Harold Rosenberg) and some of our weakest (Tom Wolfe, George P. Elliott) have gathered to debate the merits--pro and con--of this flashy and frequently unfathomable figure. The result is a generally trenchant, provocative guide to a phenomenon.