DEAN ACHESON'S LETTERS to his family and friends span, in this volume, more than half a century. They are about national and international politics, education, ambitions, illness and winter vacations. They are gossipy, sometimes biting, often warm and altogether without pomp or cant; even when they concern affairs of state, Acheson's high spirits and standards come vividly through. It is hard to think of a public figure today who could sustain, through a lifetime, such a varied and interesting correspondence.

Acheson used letters to tell his children stories about Washington. He recounts to them a speech by Ambassador Joseph Grew to the Red Cross women: "The theme -- the Red Cross stands for duty, service. The symbol of these is George Marshall -- Review of career . . . chief of staff stuck to that hard course denying himself soldier's dream of commanding allied army -- Then China . . . Peroration -- 'And this great man has only one ambition -- to retire to Leesburg and spend the rest of his life with Mrs. Eisenhower.'"

He used letters to keep his fiends up to date on his own career. To his lifelong friend, the poet Archibald MacLeish, the secretary of state wrote in 1950: "The motto for the day I read in a low, but amusing, book the other night. 'Well,' as the Madam said, 'Let's get to work, girls, the piano isn't paid for.'"

He used letters to report simple things and to pass on interesting speculations. He wrote to another cherished friend, Justice Felix Frankfurter, not only about who was up or down in Washington, but about his success in turning salvaged wood from the White House into a table. (He was a master cabinetmaker.) Acheson, who owned a farm in Sandy Spring, Md., quoted in a letter to a law partner G. M. Young's view that "Statesmen are not architects but gardeners dealing with such materials as only nature can provide."

He and Alice Acheson vacationed almost every year in Antigua, in the West Indies, where he read widely in history and fiction. But the large issues that occupied him in office, and as an advisor to several presidents, were never far from his mind and pen. The theme of Russian imperialism, and the necessity for a vigorous Western alliance to cope with it, runs through letters to his son and daughters, to friends in Europe and Australia and to the boss he deeply admired, Harry Truman.

I found those letters to Truman the most interesting in the book. They could be called "flattering" only if the word is taken to include expressions of genuine affection and esteem. Truman was courageous, decisive; he didn't mope about things. That suited Acheson perfectly. Yet in addition to the salutes he sent his old chief, Acheson did not hesitate to chide him when he went off the track. In 1957, Truman wrote for The New York Times an article of which Acheson strongly disapproved:

"I wish it were possible for us to coordinate our efforts a little better on foreign policy matters . . . . Your article says that 'Congress has no alternative but to go along with the president [Eisenhower] in this program.' If this is so, then I spent four useless hours before the Foreign Affairs Committee and a good many useless days of work in devising what I thought an excellent alternative, and one which was thoroughly in accord with steps which had been taken during your Administration."

Later on, in 1960, he is even stiffer with Truman, in a letter proposing that "we partisans" make a treaty "as to what we will not say to the press:

" . . . About Foreign Policy:

(a) For the next four months do not say that in foreign policy we must support the president . . . .

"This just isn't true. One might as well say 'support the president' if he falls off the end of a dock. That isn't a policy. But to urge support for him makes his predicament appear to be a policy to people who don't know what a dock is."

" . . . About the Negro Sit-in-Strikes:

(a) Do not say they are Communist inspired. The evidence is all the other way, despite the alleged views of J. Edgar Hoover, whom you should trust as much as you would a rattlesnake with a silencer on its rattle . . . . Your views, as reported, are wholly out of keeping with your public record . . . . If you want to discuss the sociological, moral and legal interests involved, you should give much more time and thought to them."

What an interesting relationship theirs was -- the elegant, Yale-trained diplomat and lawyer, and the plain midwestern politician. Quite apart from their shared views or disagreements, their association was rich with both irony and fidelity: Acheson suggesting lines of policy to Truman, applauding him for perspicacity when he adopted those policies, remonstrating with him (as being untrue to himself) when later he expressed the more conventional views of an elderly ex-president. Truman was the sturdy instrument of a world-view that Acheson helped, as much as anyone, to conceive; yet he was also, and simply, the boss to whom Acheson was always faithful.

About other presidents he was much less pleased. There are flashes of anger toward Eisenhower and dulles, particularly towards the latter's purge of the State Department: "Dulles' people seem ot me like Cossacks quartered in a grand old city hall, burning the panelling to cook with." The Kennedy administration he found preoccupied with its image. "This is a terrible weakness," he wrote Truman. "It makes one look at oneself instead of at the problem. How will I look fielding this hot line drive to shortstop? This is a good way to miss the ball altogether." Johnson, he told Truman in 1959, was "the ablest man in national public life today . . . a giant among pygmies." But by 1966 he thought him indecisive and self-pitying; "he is both mean and generous, but the meanness too often predominates." He had scorned Nixon for years:

"But Knowland and Nixon, that's whoI'd like to see on Quemoy or Matsu" -- but in 1969 Nixon wooed him with requests for advice, and Acheson responded with praise in letters to friends.

Among Friends is the epistolary record of a large intelligent life. Acheson chose public service, not because there was anything "divine or sacred about public service . . . but because there is no better or fuller life for a man of spirit. The old Greek conception of happiness is relevant here: "The exercise of vital powers along lines of excellence, in a life affording them scope.'" On the evidence in these letters, his was such a life, generously shared with his friends and now, in this book, with the rest of his countrymen.