"THE TOWN PLANNER needs the aid of the poet," the young Lewis Mumford advised Clarence Stein, when Stein was planning the garden city that became Radburn, N.J. That advice captures the essence of Mumford's unique role in American letters.

Mumford's towering contributions as a writer defy easy categorization. Indeed, in this newest book we become privy to his continuing self-consciousness concerning his special but somewhat ambiguous place in the professional universe. As a young man he resented being pigeonholed under the "epithet" of "sociologist." Later he was called an architect and city planner, "and even -- a misnomer if not a final insult -- an unnbanologist." Mumford approvingly quotes a friend's early observation that he was wise to avoid specializing in any field lest he end up "head of a Bronx League of Progressive Citizens, agitating for a new sewer system." For some time he says he was "uncertain... whether I would be a sociologist, a dramatist, a critic, or a philosopher until I found the coat of many colors that actually fitted me."

That coat is on display in this anthology of selected essays, letters, criticism, random notes, articles, poetry, semi-autobiographical fiction -- most of it previously published. It is intended to show the fabric of an extraordinary life of 80 years; and to reveal a man who, as he puts it, is a generalist who "has specialized in the art of being alive." This is not, unfortunately, an autobiography. That is yet to come.Mumford provides only tantalizing glimpses of his life experiences: the heights and valleys of a long marriage, the pain of a son lost in war, the intellectual and emotional relationships with men and women of letters and public affairs. It is these pieces of the coat that provide the warm, vivid hues, against which the more intellectualized and less autobiographical material appears cold and pale.

Here is a man who began to write random notes to himself at the age of 16 to capture ideas on the wing, keeping a pad and pencil within easy reach indoors and out. This habit enabled him to write Green Memories (1947), the evocative story of his "shyproud" son Geddes, killed in combat in World War II at 19. The all too few excerpts from this work and others from a family album of notes reveal the character of a father and husband whose poetic insights have prodded and informed thoughtful architects and planners for generations. For example, memories of his son bring back recollections of the role of the kitchen in family life:

"The kitchen remained the center of our actions and our affections: indeed, one could not pass from one part of the house to the other without going through it. No good architect could have planned the place so badly; but from a family point of view, no good architect would have had imagination enough to make such a happy, sociability-provoking blunder."

Nevertheless, eyes that may water upon reading the touching memories of family life may struggle to remain open when pondering some of the letters and essays in this lengthy volume. Too many of them touch on issues and people less germane to Mumford's special strengths and the interests of his wider audience.

But the book nonetheless reflects the courage, humanity and brilliance of a man who has partaken of the "feast of life." Mumford is a philosopher, but a philosopher with mud on his shoes. He has given a higher meaning and context to the often mundane work of designing and building clties. He has been close enough to the dally world of action to suppose that his ideas have made a difference among decision makers.

His opposition to the cult of technology, his continual plea for human scale, his respect for the land, are now more conscious constraints among those who design human settlements. In this book, his early and pointed arguments for intervention in World War II and his similarly early and out-spoken opposition to the Vietnam disaster ring again in proud and clarion tones.

Because he has not flinched from facing realities, Mumford notes that he is often dismissed as a prophet of doom. Yet he retains a curious quality of hope and pessimism. "If the forces that now dominate us continue on their present path," he writes (his italics), "They must lead to the collapse of the whole historical fabric, not just this or that great nation or empire."

In the face of this sobering warning, perhaps we may take some heart from a 1924 Mumford letter to his wife, Sophy, observing that "you incline to understatement and I to emphasis." Fifty years later he tells Sophy that he. would die happy if his tombstone could be inscribed "This man was an absolute fool. None of the disastrous things he predicted ever came to pass." Because the times have often caught up with Mumford's wisdom, let us hope he is around to counsel us for years to come, even at the expense of making him seem foolish. CAPTION: Picture, Self-portralt of Lewis Mumford at 29