IT IS HARD TO believe that 25 years have passed since Adlai Stevenson first unleashed his eloquence on national audiences. And what a special eloquence it was! Not the silvery cascades of cliches that went down so smoothly at rallies of the party faithful, but calls to greatness. He clothed immediate issues in long-term principles, and translated voter appeal into recitations of the democratic credo. He refused to allow American to see themselves as anything but heirs of a noble past, primed for struggle in a dangerous present. No wonder the electorate twice turned him down in favor of a soothing martial patriarch. Yet even in defeat, he lifted the level of discourse high. In Hubert Humphrey's words, "Adlai gave us all a little class."

Martin's biography has a class of its own, based on thoroughness and closeness. A campaign advisor and friend to Stevenson, he was given full access to the enormous collection of papers accumulated by "the Governor," who discarded nothing. Martin also interviewed, in depth, some one hundred of Stevenson's intimates. The result is a kind of "official" biography in the sense that almost everything in it is reflected through the eyes of Stevenson and his friends. Since they were all fearsomely articulate, every page sparkles with good quotations embodying the perceptions of some of the era's "best and brightest" men and women, in whose company Stevenson took such pleasure.

There are pitfalls to such histories. In the long run, they must be supplemented by works which embrace more of the viewpoints and testimonies of their heroes' opponents. But the worth of this book will remain unchallenged. It continues where Martin's first volume, Adlai Stevenson of Illinois, left off - the morning after Election Day, 1952. It takes him through law practice and politics to the end of 1960, and then his four years of service as our permanent ambassador to the UN. It seems safe to say that the two volumes will be the foundation for all future interpretations. Despite the gravity of this recommendation, the book is highly readable. Martin, a professional writer, keeps his subject alive and moving as he threads his way through a mortuary of now-dead issues. (What will young readers make the names like Quemoy, Katanga and Goa, one wonders?)

Though done with the cooperation of Stevenson's heirs, this is not an adulatory biography. True, it radiates admiration. Martin believes that Stevenson was a prophetic conscience in a time of need.As chief spokesman for the opposition to Eisenhower, he fought for priorities that would put public needs on a par with private consumption. In foreign affairs, Stevenson edged public opinion away from cold-war confrontation, and towards control of nuclear arms, medication of conflicts, and sharing of resources with new, nonwhite, and developing nations. In effect, Martin shares the view of Arthur Schlesinger Jr., who has written elsewhere that whereas in 1948 the Democrats' motto had been "You never had it so good," by 1960 most would-be Democratic nominees "and Kennedy most of all, were talking in the Stevenson idiom and stressing peril, uncertainty, sacrifice, purpose," Kennedy was "the heir and executor of the Stevenson revolution."

Despite this favorable verdict, no evidence is suppressed of the ideological and personal flaws in Stevenson's liberalism. He was hesitant in his support of the civil rights revolution. He blamed social stagnation on popular complacency induced by Eisenhower, but he did not probe to find and attack those powerful lobbies which used that mood to shelter their prerogatives. Though not a brinksman, he saw communism as a threat to the West greater than any "since Islam retreated from Europe." And in the UN, he sturdily supported American shows of force in the Caribbean and Southeast Asia that filled some fellow liberals with what later turned out to be well-founded misgivings.

These pages show him so essentially conciliatory, in fact, that they will reopen the never-ending debate as to what kind of president he would have made. Could he, with his unsuspicious faith in good intentions, have dealt toughly with the CIA, the FBI, the congressional and Democratic party bosses, the military-industrial baronies? Could he have escaped defeats that overtook harder men like Kennedy and Johnson? One doubts it.

The concluding portion of the book is likely to stir controversy among those who knew Stevenson well, and who seem to believe that Stevenson was one more victim of fame. Before 1952 he was relatively unknown. Thereafter, when he traveled to Africa, Latin America, Europe and the Soviet Union, he was always admitted to the society of the mighty.Press conferences gathered at his every stop. Editors and publishers clamored for his prose. There was no way back to obscurity. But alas, there was no way up either. He was finished as a presidential contender after 1960. The UN post was symbolically important but Ambassador Stevenson was largely excluded from the formulation of the policies he had to support. And so, according to George Ball's recollection, "Adlai was a terribly unhappy man. History had passed him by. His life had passed him by. He had no place to go."

Was this true? Surviving Stevenson associates alone can answer with full knowledge. But the record is, in fact, saddening. From 1961 to 1965 Stevenson not only worked, but traveled at a frenzied pace, continuously factfinding, lecturing, writing. He ate and drank heavily, and socialized - sometimes in pursuit of diplomatic duties, sometimes merely for amusement - until he grew exhausted and unable to refresh his mind with books or his overweight body with unmedicated sleep. Doctors told him bluntly that he was killing himself. He ignored the warnings, and dropped dead, of a stalled heart, on a London street at age 65. What was he pursuing? Or being pursued by? There is this to consider as a possible answer. In 1964 he wrote his good friend, Marietta Tree (who was walking at his side when he died) that he was "blinded by the sunset and groping for the path down." Had he found it?

But let us turn to the verbal legacy of the man, in Volume 7 of The Papers of Adlai E. Stevenson, 1957-61. The entire emerging series is under the able guidance of a staff headed by Walter Johnson, one of those who originally drafted Stevenson for the Presidency in 1952. These papers, too, are semi-official, in that they require the family's clearance (subject to an arbitration procedure in case of disagreements), and that some letters have been omitted or edited if they would cause "unnecessary anguish to people still living. "Those which remain are beautifully printed, intelligently and economically explained, and a reader's delight. Stevenson was a chronic correspondent, and his lucky men and women friends (there were many of the latter, preferably married and several at a time) got missives that were witty, humane and stimulating. The letters and the printed speeches remind some of us why we were so taken with the man, whom Agnes Meyer called one of the last "artist-statesmen" in an era of "engineering-statesmen."

Some of the very best - those of 1952 or of 1954, the nadir of McCarthyism, are not in this volume. But he could still strike the old sparks in 1958, for example, when he told one audiences: "If freedom means ease alone . . . the steady cult of the trivial and the mediocre . . . we may keep for a time the forms of a free society, but its spirit will be dead. "Or in 1960, when he told a University of Virginia gathering that Thomas Jefferson's faith in "the intelligence as well as the virtue of the peopl" confronted us still with "the overwhelming challenge, the exciting opportunity, to show the world that the American revolution still belongs to all mankind." He was a man whom you felt better for having listened to. These literary monuments show why.