No logic can account for the astounding beauty of "Black Folk Art in America: 1930-1980," which goes on view today at the Corcoran Gallery of Art. This show is vast and vivid, important -- and uncanny. Its finest works suggest a set of sudden miracles, of inexplicable leaps from poverty, from loneliness, toward the very core of contemporary art.

How can unknown art so strong exist? How did these 20 artists --these laborers and barbers, most old, poor and untutored, working by themselves in the alleys of this city, in the basements of New Orleans or in tattered southern shacks -- produce objects of such power?

Corcoran associate director Jane Livingston and curator John Beardsley, who put this show together with awe and high ambition, know no easy answers. By the time they visited the Louisiana house of Sister Gertrude Morgan, the fact that her small lawn was covered not with grass, but with four-leaf clovers, struck those searching scholars as "somehow perfectly unextraordinary." By that time they had grown attuned to the amazing. No knowledge of old Africa, or of slave-era folk art, of "devil jugs," walking sticks, voodoo charms and quilts explains the radiant rightness of the relatively new objects in this show.

The artists credit God, His commands, visions, dreams.

Florida's Jesse Aaron (1887-1979) was already in his seventies when, as he reported, "in 1968 three o'clock in the morning, July the fifth, the Spirit woke me up and said, 'Carve Wood' one time." Nashville's William Edmondson (1870-1951), whose limestone animals and angels are among the richest statues in this show, "was out in the driveway with some old pieces of stone when I heard a voice telling me to pick up my tools and start to work on a tombstone. I looked up in the sky and right there in the noon daylight He hung a tombstone out for me to make." Bill Traylor, born a slave in Alabama in 1854, was already 85 when he suddenly began to make his extraordinary drawings. "It just came to me," he said. Steve Ashby (1904-1980), who made his witty, worldly figures in nearby Delaplane, Va., was similarly inspired. "I wake up with an idea that won't let me get back to sleep," he said. "So I get up and make that idea." Sister Gertrude Morgan (1900-1980) often spoke with God. So did Washington's James Hampton (1909-1964), whose "Throne of the Third Heaven of the Nations Millenium General Assembly," an extravagant environment of gold and silver foil, was found in a locked alley garage here not long after he died.

Cynics may, of course, smile at such revelations, and at the art they label, almost always patronizingly, "innocent," "naive," "primitive" or "folk." But Livingston and Beardsley refuse such condescension. Livingston sees the art that they have chosen "not as the byproduct of the fantasies of eccentrics or naifs, but as the achievement of artistic masters."

The impulse for the show, Livingston says, was a scholarly response to "hip New Wave esthetics." Her essay in the catalog cites "the very fashionable, exceedingly urbane and incipiently decadent 'bad' or 'new image' or 'new narrative' art" now so much in vogue. Her stance is not equivocal. "Much of even the best of this consummately sophist art," she writes, "pales in comparison to the nominally 'naive' work we are confronting here."

This show compels agreement. No opera singer who tried to reproduce a blues by Robert Johnson would call his singing "primitive." No artist who examines the strongest works on view here -- Edmondson's limestones, Aaron's totems, Ashby's sophisticated figures, Traylor's startling silhouettes, or the wondrously raw paintings of South Carolina's Sam Doyle (born 1906), or the eerie landscapes of Chicago's Joseph Yoakum (1876-1972) -- would call such art naive.

There are more than 400 works on view, perhaps a few too many, and it is not surprising that the weakest of them suffer. But the most impressive -- a "Walking Stick with Figure" by Louisiana's David Butler, Edmondson's stone angel, Ashby's small self-portrait, and that terrifying image, also a self-portrait, by Mose Tolliver of Alabama -- leave the viewer stunned. Sometimes one can almost see "high" art's modern masters winking in these objects. That Ashby is as witty as a drawing by Saul Steinberg, that Butler seems as free as a sculpture by Picasso, that unforgettable Tolliver is as raw as a de Kooning.

Livingston and Beardsley contend, again convincingly, that such folk art is a major episode in recent American art history. They argue further that despite the work of such artists as California's Simon Rodia, who constructed the Watts Towers, "fully half of the truly great artists in the recent American folk genre, from the early 1920s to the present, are blacks and predominantly Southern blacks."

Though the line is surely blurred, black folk art, like black folk music, differs in important ways from that produced by whites. White folk art, like white ballads, tends to stress a line of narrative. These objects, like most blues, instead frequently portray not a story but a feeling. And unlike most white folk art, and so much modern craft, the objects here refuse the pretty and the cute, the sweet, the sentimental.

It is eerie to remember that such astounding black musicians as Robert Johnson, Lemon Jefferson, Leadbelly, Louis Armstrong, Charlie Parker, Thelonius Monk and John Coltrane -- whose art appears to trace a rise from the archaic to high sophistication -- were all alive at the same time. But music is communal, Leadbelly heard Jefferson, Coltrane studied Parker, while the artists in this show all came to art alone. Ashby, it is true, did front-porch puppet shows in Delaplane; Sister Gertrude Morgan showed her paintings on the street; Butler's painted whirligigs were shown outside his shack. Though these works, and many others here, were made to move an audience, a close-knit black community, the artists who produced them worked in isolation. This show calls into question much we have been told about the function of art's labels, its mission and its schools. "The artist," said William Carlos Williams, "is as old as the fish." This show, which calls to our attention an episode in recent art which, in Livingston's phrase, "is unaccounted-for, sociologically, and unknown, art-historically," reminds us one can find great art in most unlikely seas.

This evocative, original and memorable show has been handsomely installed, by Alex Castro, in a sequence of small galleries on the Corcoran's second floor. Its catalog is fine. It will travel to Louisville, Brooklyn, Los Angeles and Houston after closing here on March 28.