Although it went unnoticed almost everywhere else, the centenary of Sinclair Lewis was celebrated last week in the Minnesota town of Sauk Centre, which Lewis had fictionalized as Gopher Prairie in his notorious satire of small-town American life, "Main Street." That the occasion caused so little interest elsewhere is sad commentary on how quickly, and how far, Lewis' reputation has declined since his death in 1951.

Lewis was born in Sauk Centre on Feb. 7, 1885, into a generation that a couple of decades hence would leave the small towns for the cities in a vast horde of questing, ambitious young men and women. Lewis himself was one of these, and like so many others he ended up in New York; but unlike the others he never became a wholly metropolitan man, and the vision of provincial life that he carried in his mind eventually became the principal impulse behind his powerful and provocative fiction.

That fiction, as Joseph Epstein has noted, now lives -- to the extent that it lives at all -- in the classroom, where "Main Street" and "Babbitt" and "Arrowsmith" are still taught, though more often perhaps as sociology than as literature. But outside the classroom there seems now to be no appreciable audience for his work. Helen Hooven Santmyer's " . . . And Ladies of the Club," which became a great best seller last year, was written in protest against the portrait of small-town life that Lewis drew in "Main Street"; but how many of those who read it in 1984 remembered, or even had read, the novel that inspired it?

The explanation you'll get in literary or academic circles for Lewis' decline is that he really was not a very good writer and that he was incapable of drawing up a coherent plot. The second is to some extent true, but the first most emphatically is not. Rereading the aforementioned three novels last week for the first time in years, I was struck by how lively Lewis' prose remains and how penetrating his satire still seems. The early 20th-century Middle Western argot that his characters speak now seems irretrievably dated, but the energy of the novels is just about as impressive now as it was when they first came to the attention of a startled nation.

It's difficult for us to imagine just how startled the nation really was, for "Main Street" and "babbittry" have for so long been part of the language that we take them, and the assumptions they suggest, for granted. But when those books were first published -- in 1920 and 1922, respectively -- they seemed as radical to readers as "Portnoy's Complaint" did two generations later. Never before had the American small town and the American businessman come under such withering attack. The books could not have caused a greater sensation had they been banned in Boston -- as, in fact, Lewis' satire of evangelical religion, "Elmer Gantry," was in 1927.

What Lewis saw on Main Street was "an unimaginatively standardized background, a sluggishness of speech and manners, a rigid ruling of the spirit by the desire to appear respectable." This was "the contentment of the quiet dead . . . dullness made God." As for its inhabitants: "A savorless people, gulping tasteless food, and sitting afterward, coatless and thoughtless, in rocking-chairs prickly with inane decorations, listening to mechanical music, saying mechanical things about the excellence of Ford automobiles, and viewing themselves as the greatest race in the world."

Lewis was no less stinging when he moved from Gopher Prairie to Zenith, principal city of the state of Winnemac, and studied "the religion of business" in "Babbitt." In the provincial city, just as in the provincial town, Lewis found little except "mechanical" lives and oppressive conformity: "Just as Babbitt was an Elk, a Booster, and a member of the Chamber of Commerce, just as the priests of the Presbyterian Church determined his every religious belief and the senators who controlled the Republican Party decided in little smoky rooms in Washington what he should think about disarmament, tariff and Germany, so did the large national advertisers fix the surface of his life, fix what he believed to be his individuality."

This sentence alone should make clear that, however much in "Babbitt" may seem dated, all too much of it remains all too painfully pertinent. The same is true of "Arrowsmith," which is the story of a bacteriologist who finds that his yearning to do pure research is complicated at all turns by individuals and institutions that want to use science for their own immediate, selfish ends. Physicians, public-health officials, foundations -- all follow "the slimy trail of the dollar," forcing Martin Arrowsmith to compromise and, in the end, to make a hard choice between life in the laboratory and life in the world.

Like a few other writers of his period, most notably Theodore Dreiser and Frank Norris, Sinclair Lewis wrote about people, places and subjects that have now almost disappeared from American fiction. He wrote, for example, about business, around which American life is inextricably constructed yet which is now beneath the contempt of our writers of fiction. He wrote about life in the world as Americans actually live it, and he did so with a powerful belief in the importance of his subject. His view of America was mordant, yet it was also unexpectedly loving; there is a tenderness in all three of these books that catches the reader unawares, and imbues them with a humanity that makes their satire all the more penetrating.

It is true that Lewis was reviled by many in his time, but he was honored by even more. He was awarded a Pulitzer Prize in 1926 for "Arrowsmith," but, in a fit of petulance, refused it. Four years later, though, he accepted his Nobel Prize for Literature with gratitude and glee. As the first American to win that honor, he took it upon himself to speak, in Stockholm, for the emerging literature of his country: To attack the academy ("Our American professors like their literature clear and cold and pure and very dead") and to praise, by name, those younger writers who were beginning to shape what we now think of as American literature.

Lewis was not a great novelist; there is no getting around that. But he was a supremely perceptive student of American society who recorded what he saw with a sharp, telling pen. After "Elmer Gantry," in 1927, and "Dodsworth," in 1929, he published nothing of real consequence; but what he achieved in his five major novels should be neither underestimated nor forgotten. His centenary is a far more important milestone in American letters than the events in Sauk Centre suggest; it is the entire country, not merely a small town in Minnesota, that should be applauding him and his work.