APPLES IN a pail, roses in profusion, a shelf of books, a candlestick, a rifle on a door. Why is it that these homely things, when carefully portrayed in paint, evoke a sense of wonder? What pleasure in the palpable, what joy in the accessible, or gratitude or dread, lends these focused images the aura of the icon?

Americans love still lifes. So does William H. Gerdts.

It was William Gerdts who chose (and in some cases discovered) the 123 pictures on display in "Painters of the Humble Truth: Masterpieces of American Still Life, 1801-1939," the touring exhibition that is now on view at the Baltimore Museum of Art. Its tightly rendered pictures of fruits and flowers, hunting horns, letter-racks and game, often fool the eye. But they do not fool the mind.

. . . the roses had the look of flowers that are looked at. . .

T.S. Eliot knew that even the most lifelike still lifes do not look like life. It is their artifice that moves us. The term, in French, is nature morte--"dead nature"--for all the paintings here sing of time suspended and, distantly, of death.

We know that blossom painted with such convincing skill by Martin Johnson Heade, that fleshy white magnolia, was a flower bound to wither, and that Winslow Homer's fresh-caught trout, hanging on a twig, were not fresh for long. The poignance of that knowlege penetrates these pictures, but it does not make them fey. Their modesty protects them. William Michael Harnett's hourglass and skull, the vegetables of Charles Demuth, Georgia O'Keeffe's lilies and David Johnson's pears, are symbols, if you like--of freshness or fruition, of bounty or decay--but they are symbols without pretense. The still lifes Gerdts has brought us share, above all else, a loyalty to fact.

They shy away from summary and are anchored to the real. Their beauty is the beauty of the sharply seen specific. Their virtues are the virtues of the work of William Gerdts.

He is a special kind of scholar. Once an art professor at the University of Maryland at nearby College Park, he teaches now at Brooklyn College and trains doctoral candidates at the City University of New York. He is a teacher of distinction. A devourer of documents, he distruststheoretics. While other art historians, more speculative specialists, stalk the dim, elusive poetry of America's old art, Gerdts commands its prose.

His memory for facts, for details and dates, for statues and for pictures, is accurate and awesome. It is probable that William Gerdts knows as much about America's art history as any man alive.

"He has at his command more visual information than anyone I know," says Doreen Burke, assistant curator of painting and sculpture at the Metropolitan Museum of Art. "It is all there in his head, packed in ear-to-ear."

"If you have a question, a difficult question, about a work of art," says Theodore Stebbins of the Boston Museum of Fine Arts, "Bill Gerdts is the first person that you go to. His head is full of lists. He makes the rest of us seem lazy. He is an extraordinary figure, a superb correspondent, a devoted, loyal teacher. But no one walks on water. It sometimes seems he knows so much that he's afraid to generalize. And he is, at times, difficult to work with. He does things that he shouldn't do, and I have seen him be touchy and acerbic. But in terms of care for accuracy he has set new standards."

"He has an archival mind, but archival with intelligence," says John Wilmerding, curator of American art at the National Gallery of Art. "He digs up little-known facts, exhibition records, forgotten publications. He is always turning up useful information. The danger in that effort, and I think he would agree, is that if you care too much for data you can lose connoisseurship."

"It is an obsessive-compulsive kind of thing," says Bill Gerdts of the drive he calls "my need for information." In recent weeks he's spent whole days Xeroxing 19th-century periodicals in the Library of Congress. He is 53 years old, a slim and energetic man, capable of being vain in unexpected ways, kind as well as cutting, proud as well as modest.

"In college, at Amherst, I remember going to the fiction section of the Library and reading all the 'A's.' I got into the 'Bs' before my graduation. I saw every Carole Landis Film ('I Wake Up Screaming' was her best), and read all the books of Henry James--in the order that he wrote them. I do things that way.

"I sometimes wonder if I love information for its own sake--but I know I also have this Puritan compulsion to do something with my knowledge. Today I feel it all falling into place. Today it seems to work. I am seeing things in art I never saw before, things I would have missed had I not amassed all that information."

Gerdts has been around. Unlike many academics, he has worked in art museums (in Norfolk and in Newark after graduate school at Harvard); and unlike most museum men he has worked in the art market. After leaving Maryland, he spent 18 months with a commercial gallery, the Coe-Kerr in New York. He is also a collector. The walls of his apartment are skied with first-rate paintings, many of them still lifes, some of which he bought for $35 or $50 or $200. Seven of his paintings are included in his show.

While many scholars in his field specialize in one subject or another, Gerdts has tried his hand at many. His scores of articles and catalogues, some of them quick hits, show his restlessness, his range. Gerdts has written on American impressionism, tonalism, luminism and cemetery monuments. He has published two books on American still life (the first one was co-authored by his student Russell Burke, then a 19-year-old undergraduate at the University of Maryland, now president of Phillips, the Manhattan auction house). Gerdts has also written on 19th-century sculpture ("The Marble Resurrection"), on Washington Allston, Joseph Stella, "The Great American Nude," and "Painting and Sculpture in New Jersey" ("from the start to Leo Dee--who married my first wife.")

He's been lucky in his timing. He finished graduate school at Harvard in 1952, just in time to use his methodology in a field of art history that, until his arrival, had been only lightly mined.

America's discovery of America's art history is relatively recent. The first generation of Americanists, those who came to prominence in the 1920s, the '30s and the '40s--Lloyd Goodrich, John I.H. Baur and Edgar P. Richardson among them--did pioneering work on Homer, Eakins, Ryder, Allston, Eastman Johnson and other major figures. But they left much unexamined. "Richardson's book on Allston dealt with various concepts of the 'romantic artist' and that sort of thing," says Gerdts. "I dealt with where he was on Jan. 4, 1815 (he was attending his sick wife, and perhaps chasing sailors). I hope the painter is not lost in all that information."

Gerdts may well have been the very first historian to study for a doctorate in American art history, a field once considered but a minor province of European art. Younger than Goodrich and Richardson, he is old enough to have influenced, and often trained, the many young historians who nowadays are digging out the long-neglected, often minor, artists of our past. Gerdts, as Russell Burke points out, is a kind of link between those two generations.

One sees that in his still life show. The major painters represented--John Peto and the Peales, Homer and Harnett, O'Keeffe and the rest--are joined in the exhibit by curious minor figures--Arnoud Wydeveld, Andrew Way, Fidelia Bridges, D.M. Bunker, Eliab Metcalf, and a dozen more--of whom few of us have heard.

Its range, its catholicity, is both a major virtue and the central flaw of Gerdts's exhibition.

Its catalogue, which builds on the work he did with Burke, may well be the best book yet published on its subject. Handsome, thorough, readable, it will be a useful textbook for many years to come. But in some important ways it dims the exhibition. Many of the finest pictures it discusses, the Copleys, for example, were not available for loan.

Gerdts knows that he has been accused of liking amassed facts so much that he does not bother to carefully distinguish between the greatest works of art and those that don't quite make it. Gerdts will say of Stebbins that "his primary interest is esthetic quality," and add, parenthetically, "I'd say mine is not." It is not that he can't see it, he has a superb eye. But the question of connoisseurship damages his show.

Its subtitle--"Masterpieces of American Still Life, 1801-1939"--seems to be ill-chosen. There are minor works aplenty here, and its 20th-century section is strangely disappointing.

Gerdts has taught us much. When he discovers parallels between a Raphaelle Peale still life and Greek-revival architecture, or between a crowded Severin Roesen and a plush Victorian parlor, or between the art and biography of Peto, his point of view is thrilling. But an old, disturbing doubt nags his exhibition. One cannot help but think that a "masterpiece" exhibit of European still lifes, a show of Chardin and Cezanne, Matisse, and Morandi, would blow this one away.

John Mahey of the Philbrook Art Center, Tulsa, helped organize "Painters of the Humble Truth." It will travel to the National Academy of Design, New York, after closing in Baltimore on April 25.