Harry Reasoner's shirtsleeves memoirs of his ""first twenty-five years in television news""--tantamount to the ""first twenty-five years of television news""--leads off with some great, base-touching one-liners, settles into a fascinating backgrounder on the very early days, and then just sort of dips and swoops through the Big Time years. But the offhand Reasoner charm makes for easy going, regardless; and there are those heroic beginnings--when TV news was trying to be what the newsreels never had been, a real news medium. ""We had to invent things before they were simple."" At CBS News, from '56 on, Reasoner and other then-unknowns ""who knew and liked film. . . who felt at home in a thirty-second report,"" began to go out on the stories with the cameramen; and then, as the vening news became more important, with the likes of Doug Edwards and Bill Downs. Nothing undignified--still: ""We wanted to be a CBS News Correspondent. Good Lord, that was Murrow's title."" And in '57, Reasoner made it: ""The first to be named out of television news."" How It Was: an eight-o'clock call at home, in Connecticut; a plane from La Guardia late that night; a morning charter to the site; and ""try to figure out how to make a story of the incident that justified all the charters and rushing and sleeplessness."" And catch that evening's broadcast. In Florence, S.C., after a stray-bomb incident, Reasoner invented the Barber Shop Device: ""some real, evocative comments,"" in five or six minutes. After those ""fireman days,"" the fall-off begins--with Little Rock, which Reasoner touts as a television story, then tells as History--as a victory for the ""moderate bourgeoisie."" And then it's a motley: professional pique; domestic tribulations (eventually, a divorce); unnamed other women; always a ""co-something"" (discretion re Barbara Walters); LBJ; 60 Minutes (the grind, the satisfaction); leaving CBS ""heartsick"" after seven years--and coming back. Says his new wife, after the first, burial-of-Pope-Paul broadcast: ""You sounded inappropriately joyous."" So: lots of zest, shrewd pacing, spotty reporting.