A sometimes stirring but numbingly overargued and long-winded defense of television. As it has expanded from its first lonely trinity of networks to the much-promised 500 channels, television has fallen into increasing disrepute. Quite a change, as New York magazine TV critic, and former New York Times book critic, Leonard (Private Lives in the Imperial City, 1979, etc.) carefully details, from the carefree pioneer days, when TV was almost unanimously welcomed into the national culture. Now it is held responsible for all manner of societal ills; politicians decry programmed sex and violence; V- chips are in the offing; and even the notion of a national culture has broken down. But as Leonard copiously argues (long past the point of convincing), the boob tube is not as bad as it's cracked up to be: ``A medium capable of China Beach, M*A*S*H, St. Elsewhere, Northern Exposure, Homicide, and The X-Files has less to be ashamed of than many of its critics do, and most of its competition.'' Then, just to drive his point home, Leonard looks for the good in every type of programming TV has to offer. From mysteries to movies of the week to talk shows to medical dramas, Leonard draws a madly elaborate portrait of a medium deeply and positively engaged with the issues and circumstances of our lives: ``How is it . . . that our politics and culture got so mean while television was asking us night after night to be nicer to women, children, minorities, immigrants, poor people, and strangers?'' But even Leonard's rousing, acerbic style can't pardon his excesses: 40-plus pages on police shows, much of it recapitulation of plots and characters, 30 pages on shows about AIDS--he just keeps going, and going, and going.