ONE ALWAYS PICKS UP the autobiography of a public man with special curiosity. Is there a private person who has been hiding in there all these years, wildly crying to be let out? Will there be a different timbre to a voice that is not funneling ghost-written words through a microphone? Usually, alas, there is not much difference (perhaps because ghostwriters often do the autobiography as well as the speeches.) The statesman baring his past in print is pretty much the same we have heard on the hustings.

Such is the case with Grassroots. It is not likely that any readers will change the images they formed of McGovern in 1972 as a result of turning these pages. thise who then thought him essentially decent, truthful and compassionate may take comfort in this self-justifying personal history. Those who found him preachy and simplistic will discover that the evangelical aura has not evaporated.

The opening sections, for example, sound like a political testimonial to the virtues of birth and rearing in Depression-scarred South Dakota, and higher education in a small college there. McGovern then describes his courtship and marriage, followed by World War II bomber-pilot service, in a somewhat flat style that seems to make them almost indistinguishable experiences.

After the war, he began, in fact, to study for the ministry, inspired by his preacher-father's example and the discovery of the social gospel. But he and his wife both had reservations about their adaptability to pastoral duties. He turned instead to the study of history, took a doctorate, and might have ended obscurely teaching the American past to students at South Dakota Wesleyan.

But Northwestern Univeristy's graduate history faculty had transmuted his South Kakota Republicanism. In 1948 he was a delegate to the Progressive Party convention that nominated Henry Wallace. Four years later, the rhetoric of Adlai Stevenson Kindled him into writing letters of praise in his local paper. This stance was so rare in South Dakota then that the state's Democratic chairman sought out the young professor and urged him to become the, party's executive secretary. Promptly, McGovern accepted and began a full life in politics to the exclusion of all else - including, he candidly admits, shared and attentive time with his growing children.

It is at this point that the book is warmest and most akin to life. Building up South Dakota's scrawny Democratic vote involved long, lonely drives in aging autos, seeking out hamlets where some local "oddball" might be cultivated for a small contribution. It meant living on doughnuts and coffee furnished at receptions; painstakingly building one's own files of past and potential local workers; even peddling campaign buttons on the street to raise the price of a tankful of gas or a hotel room. It was political barnstorming, recalled with a humorous self-awareness that is rare in the rest of the book. McGovern unhesitatingly includes the story of how he borrowed a "Democratic" donkey to exhibit at a state fair in competition with a zoo elephant secured by the Republicans. The beast quickly urinated on an unoffending nun and bit the hand of a child before the idea could be abandoned.

By 1956 McGovern had sought and won a seat in the House of Representatives. He zips through his career there, then as Food for Peace director under John F. Kennedy, and then in the Senate. Finally he reaches the moment in 1968 when Robert F. Kennedy had been killed, and he suddenly inherited many of Kennedy's bereaved and leaderless delegrtes in a holding operation. Suddenly he was on stage as a presidential possibility. In describing the following four years, however, he dashes any readers' expectations of a "now-it-can-be-told" series of revelations. He tells us little that is new about the party's rules-reform convention, which he chaired. He has only superficial accounts of the strategems and feuds of the primary campaign or the convention itself. Nor is the Eagleton affair freshly illuminated. It is no surprise now to know that McGovern foolishy trapped himself (as he immediately realized) by vowing to keep Eagleton on the ticket before fully assessing the impact of the disclosure that the vice-preidential candidate had been hospitalized for depression and mental exhaustion. Nor is it news that in this dilemma Eagelton, the cause of it, was neither gracious nor helpful.

Nor are there many inside recollections of the camlaign itself. That is understandable; the poor, frazzled, over-exhibited, perpetually-moving candidate may be the last person to know what is going on around him. But there is no evidence that McGovern has digested the lessons of his defeat and put them in perspective. He repeats his old charges that he never got fair media coverage. The reporters liked him well enough, but their hunger for "colorful" material led them to blow up mistakes and dissensions in the McGovern ranks, while the Nixon White House, with power and cunning to dominate and manipulate the media, could misrepresent and ignore McGovern's challenges.

That is true, but it is only part of the campaign story. Many elements were at work - the nature of television politics, the problems of reconciling amateurs and professionals in a "reform" campaign, the differing strategies for winning nominations and elections, the hostile reaction to the 1960s which produced a myopia that enabled McGovern to appear "radical." These are all topics on which the loser's reflections would have been more valuable than a simple assertion that he kept the faith and was right at the wrong time in history. The closing section, in fact, is a review of recent McGovern positions and activities, in language that suggests the 1980 campaign shaping up. McGovern's senate seat is at stake then. Or is his eye elsewhere? He notes pointedly that all the charges aimed at him in 1972 were also aimed at Carter, who went hn to win. Could presidential fantasies still be lurking?

It gives this reviewer no pleasure to be hard on this book. For the record I supported him in 1972 and might again - but as a candidate, not an author. Clearly Grassroots will be one of the perishable works of political reminiscence in our time. Come to think of it, how many good political autobiographies are there? How many carry the sweaty tang of the "old" politics, with its ballyhoo and folk wit? How many get inside the "new" politics of computers, image-building, and the rustle of large bills? It takes the reporters, the spectators, to create such books. The actors are too caught up in the game.