Stegner laments loss of old West; One Way to Spell Man, by Wallace Stegner. New York: Doubleday & Co. 177 pp. $ 14.95.

The great American West is going through another change, and the voice of a triple-dyed Westerner like Wallace Stegner becomes a timely stay against confusion. The United States population is tipping the continent westward. The Atlantic Basin is watching the Pacific Basin turn into the pond where the action is. America's old Western frontier becomes the new Eastern frontier for Japan. When Mr. Stegner reports on a Western regional conference whose consensus was against regionalism - ''we felt pretty much like the rest of the United States, only more so'' - all of us can be the gladder that he winnowed these essays from three decades before the West was gone.

As essayist, this honored teacher and Pulitzer prize-winning novelist may not be so trenchant as Emerson and Thoreau. But surely he fills for the West some variation of the role that they did for New England during an earlier American renaissance.

He has not edited out the repetition of favorite references and the allusions to particular audiences that betray the preparation of pieces for various occasions. But to see what engages him enough for reprise may be part of knowing the Stegner whose long lifetime epitomizes the West of which he writes.

That is, growing up Western, he ''came hungrily toward civilization from the profound barbarism of the frontier.'' He was not like another Westerner, Walter van Tilburg Clark, author of ''The Ox-Bow Incident,'' who ''possessed civilization from childhood.''

So Stegner's literary and aesthetic analyses in these essays have a sense of hard-won knowledge unlike the easy omniscience of the New Englanders. And when he writes of the urgency of preserving the land, he has a whole experience of once wider, opener spaces to put beside Thoreau's famous ''I have travelled a good deal in Concord.''

This experience embraces the glorious, sad span Stegner writes about in an essay on the gift of wilderness: from days when Americans would cite their conquest of nature and ''say in pride, 'Look what we've done!' '' - to days when they see how they have plundered their living space and ''say with an appalled sense of complicity and guilt, 'Look what we've done!' ''

It's like an echo from naturalist John Muir, who wrote of the American woods in the last century: ''That a change from robbery and ruin to a permanent rational policy is urgently needed nobody with the slightest knowledge of American forests would deny.''

Now Stegner singles out a man who sees that the wilderness, once parent and teacher, has become dependent; a man like author Wendell Berry who refuses to go on with ''the unsettling of America'' and restores hillsides, woods, and fields. ''He has made the turn that the New England Transcendalists made long before him; he has joined nature instead of setting himself against it.''

Stegner's discerning regard for art and nature comes to brilliant fusion in his essay on Ansel Adams and those photographs of mountain majesty and so many other things transmuted by Adams's eloquent light and ''simple statement of the lens.'' But Stegner can turn to the library, too, whether literally in tribute to that institution or figuratively in considering fiction, philosophy, a proliferation of vulgar language.

And when he finds, for instance, that fiction always involves simplification, he does not stop with the obvious example of stripped-prose Hemingway. He goes on to Conrad (putting the world within a ship) and even the superficially convoluted Henry James (whose characters are freed of such complications as earning a living so their moral choices can be pure).

Sometimes a few too many Stegner words for the matter at hand? Not quite enough simplification of his own? Maybe. But it's worth reading on for the nuggets and the sweep of a man who grew up in wild places and takes us with him to the kind of cold Western night on a hillside when he was face to face with the universe, when he ''was awed very early, and never recovered.''