If there is one central category in Buber's thought and life, it is that of dialogue

Buber's contribution to the unfinished contestation between the two great branches of Biblical faith has by no means been exhausted. ... PHILOSOPHER ON THE NARROW EDGE OF FAITH By PETER L. BERGER; New York Times: July 31, 1983 MARTIN BUBER'S LIFE AND WORK The Middle Years 1923-45. By Maurice Friedman. Illustrated. 398 pp. New York: E.P. Dutton. $29.95.

MAURICE FRIEDMAN, who teaches at the University of California at San Diego, brings to his biography of the late Martin Buber the results of many years of working with Buber and studying his writings. The biography, of a man who is by common agreement one of the most important Jewish philosophers of the century, is a work of careful scholarship, both in terms of the external facts of Buber's life and of the development of his thought.

It is also a work of discipleship. Mr. Friedman's deep respect and affection for Buber are evident on every page and the portrait that emerges is of a virtually flawless man. If he were writing about anyone else, one would have to wonder to what extent this portrait is a product of bias; in the business of biography one might then expect that, sooner or later, some revisionist would come along to alter a disciple's portrait. In the case of Buber, such revisionism seems unlikely. One knows enough about Buber from other sources to incline to the view that, in all likelihood, Mr. Friedman's depiction is close to the reality.

This second installment of what will eventually be a three-volume work covers a period of immense productivity in Buber's career that was also a time of soul-shaking drama and tragedy. In Germany in the 1920's Buber became a key figure within the Jewish community and on the Christian religious scene as well. It was during these years that he, in collaboration with Franz Rosenzweig, began the monumental task of retranslating the Hebrew Bible into German. During the same years he wrote several of his own influential books, was active in educational and journalistic ventures of various sorts, and was politically engaged both as a Zionist and as what was then called a ''religious socialist.''

Following the rise to power of the Nazi regime in 1933, Buber stayed on in Germany for five more years, continuing to write under increasingly forbidding circumstances and devoting much of his energy to Jewish educational activities, which he saw as a form of spiritual resistance. He finally immigrated to Palestine in the spring of 1938, to become a professor at the Hebrew University. He was 60 years old at the time, yet much of his important work was then still in the future, for he continued to write and teach almost to the day of his death in 1965.

If there is one central category in Buber's thought and life, it is that of dialogue. The word has become hackneyed in recent times, especially in religious circles. Thus it is all the more important to recapture the freshness of Buber's early writings on dialogue, by which he successfully sought to integrate his thinking on a broad variety of topics. Mr. Friedman believes (probably correctly) that Buber's major contribution was in the area of philosophical anthropology, where, very broadly speaking, he belongs with the existentialist tradition (it should be noted, though, that he was very critical of both Kierkegaard and Heidegger).

Dialogue is at the core of Buber's philosophical anthropology, as expresssed both in his most famous book, ''I and Thou,'' and in many other works. Man is defined in his very essence by his capacity for dialogue - mundanely, in the dialogue between man and man; ultimately, in the eternal dialogue between God and man. Buber's understanding of society flows from this underlying philosophical conception, as does his approach to the different problems of society with which he occupied himself during his long life. But while this view of man led Buber to emphasize community, he also insisted on the primacy of the solitary individual. He abhorred collectivism of every ideological coloration. Both authentic existence and genuine insight could only be found on what he called the ''narrow ridge,'' where a free individual, alone, tries to come to terms with truth.

It is this dialogic understanding of man that Buber found in the Biblical tradition. But dialogue also characterized his own relation to that tradition, to Judaism and to other religious possibilities. Unlike Franz Rosenzweig and many other friends of his, Buber could never fully identify with orthodox Judaism. Although passionately committed to Judaism and to his own self-understanding as a Jew, he continued to be in dialogue with Judaism from his own ''narrow ridge'' and, to that extent, he always stood both within and outside the tradition (a fact that was perceived and resented by the Orthodox). He was always a man on the margin, a man of boundaries.

The same dialogic relation characterizes his appropriation and reinterpretation of Hasidism. Buber had been greatly influenced by Hasidic mysticism, but his rendition of Hasidism, especially in his early works, has been criticized on scholarly grounds (among others, by his friend and colleague Gershom Scholem), and Buber was apparently hurt by these criticisms. The nonspecialist cannot take a position on these controversies, and, in the final analysis, they do not touch on Buber's innermost concern, which was not primarily historical but existential - the rekindling of Jewish piety in the present age.

Dialogue was also, for most of his life, his concern in terms of the relation between Judaism and Christianity - or, more precisely, between Jews and Christians. He conversed, collaborated and corresponded with some of the leading Protestant and Catholic theologians of this century, and he believed that this particular dialogue was one of the most important intellectual and spiritual challenges of the age. Buber's contribution to the unfinished contestation between the two great branches of Biblical faith has by no means been exhausted. The Jewish-Christian dialogue, in which Buber was so interested, is still in its beginnings. There is a considerable agenda still ahead and there is also very much to learn from Buber.

BUBER was not exactly a political man, and it is not unfair to say that his political engagements had an element of innocence. What is one to say, for example, of the definition of socialism, attributed to Buber by his friend Leonhard Ragaz, as ''state-free and nonviolent ... in the sense of a genuine community of men built upon love''? Yet his political activities were protected from slipping into any sort of fanaticism by his unwavering respect for the individual and his liberty, which also made him a critic of all forms of utopianism and totalitarianism.

He rejected Marxism, along with the collectivism of both right and left. He rejected the more virulently nationalistic versions of Zionism, and, from the beginning of his involvement with the Zionist movement to his final years as a citizen of Israel, he was deeply troubled by the question of Arab rights and was instrumental in fostering an Arab-Jewish dialogue late in his life. The same insistence on dialogue dominates Buber's extensive work on education (in pre-Nazi Germany he was close to a number of reform experiments in education) and psychotherapy (he influenced a considerable number of outstanding psychiatrists, among them Ludwig Binswanger). He understood both teaching and healing as dialogic activities, ''between man and man,'' and he was sharply critical of all mechanistic or technical approaches in these fields. For the same reason, he was antagonistic to those schools of sociology that understood human interaction in mechanistic terms. (There is a certain irony in the fact that Buber's professorship in Jerusalem was in sociology; there had been Orthodox objection to his professing in any field defined as religious.)

IN their translation of the Bible, Buber and Rosenzweig rendered the Hebrew kadosh not as ''holy,'' but as ''hallowing.'' Holiness, in other words, is not to be understood as a condition, but as a process. Thus, if men are called to be holy, this means that they are called to hallow the world. Dialogue is at the core of this hallowing activity. But what about those who refuse all dialogue? Buber saw Hitler as the supreme monologist, who demonically attracted men to himself but was totally incapable of responding to them. Mr. Friedman reports a curious disagreement between himself and Buber. In an earlier work about Buber, written during the latter's lifetime, Mr. Friedman had written: ''One's antagonist may, indeed, be the Devil or Hitler, but even such a one must be faithfully answered, contended with.'' In a comment Buber disagreed: One cannot answer Hitler, because in no sense could he be a partner in conversation.

No doubt Buber was correct. But Buber did respond, not to Hitler as an individual, but to the world of horror that Hitler created. Buber responded by drawing even that world into the dialogue between man and God, using the most powerful symbols by which Jewish tradition has hallowed suffering, and thereby answering the horror by the faith that the secret of all worlds is redemption. On that ''narrow ridge'' of faith Buber continues to be in dialogue with us, Jews and Christians both. PETER L. BERGER, A UNIVERSITY PROFESSOR AT BOSTON UNIVERSITY, IS THE AUTHOR OF ''THE HERETICAL IMPERATIVE: CONTEMPORARY POSSIBILITIES OF RELIGIOUS AFFIRMATION.''