Andrew Wyeth, the most popular American artist of the 20th century, died early today at his home in Chadds Ford. The creator of such iconic paintings as Christina's World and Wind From the Sea was 91.

Wyeth died in his sleep, according to Hillary Holland, a spokeswoman for the Brandywine River Museum.

Wyeth was the most famous and successful artist in a remarkable family that produced five painters in three generations, but being popular was a mixed blessing. The public loved his work, but many critics and scholars considered him an illustrator like his father, N.C. Wyeth, rather than a major artist. His work was often characterized as sentimental, the critical kiss of death.

Some years ago, an article in Newsweek magazine described him as "a great illustrator but a minor painter," to which Wyeth replied, "Probably I am. What's wrong with that? It doesn't bother me any."

In truth, Wyeth's unique aesthetic vision made critics uncomfortable, because they couldn't easily pigeonhole him, and it probably misled many of his admirers.

He appeared to be a realist who used common, easily understood visual language, yet his best paintings are complex amalgams of story-telling, symbolism, memory and deep emotion whose themes aren't nearly as obvious as they might seem.

Much of Wyeth's art could function as illustration, yet on the whole it's hardly upbeat. Pictures like Christina's World, which may be the best-known image produced by an American in this century, suggest distance, emptiness, loneliness and and desolation. The dark, somber aspect of Wyeth's art has been its most prominent feature since the mid-1940s, although it hasn't always been acknowledged.

The paintings also confirm that Wyeth was an introspective, private man, a quality that he developed as a child. He was never part of the mainstream art world, nor did he care to be. The world in which he lived and worked, and from which he drew inspiration, was tightly circumscribed; it consisted of Chadds Ford and Cushing, Maine, where he spent summers, and his family, friends and neighbors.

While Wyeth's art is very much tied to specific places and people, he usually tried to convey universality and timelessness in whatever he painted. For example, Christina's World depicts a person and a house in Maine that Wyeth knew intimately, but it's neither a portrait of the woman nor a landscape; it's a psychological construct.

This is true even of the so-called Helga pictures, which caused Wyeth and his wife considerable discomfort in the spring and summer of 1986. For 15 years beginning in 1970, Wyeth had worked with a model named Helga Testoff, a German immigrant who lived near him in Chadds Ford.

During that time, he made nearly 250 paintings and drawings of her, many of them nudes. The disclosure of the so-called Helga suite caused a sensation in the press because supposedly no one except Wyeth and his model, not even his wife, Betsy, knew of this protracted relationship.

The story of the reclusive artist and his "secret" model, which made the covers of Time and Newsweek during the same week in August, 1986, generated considerable gossip. Wyeth was said to have told his wife about the paintings when he was seriously ill and in fear of dying -this turned out to be a rumor. She, in a jealous pique, was said to have ordered them sold.

For whatever reason, they were sold, to entrepreneur Leonard E. B. Andrews, for a sum that neither side would disclose, although speculation centered on $6 to $7 million.

Andrews parlayed his collection, which he repeated characterized as "a national treasure," into a major traveling exhibition organized by the National Gallery of Art and a book. In late 1989, he sold his "treasure" to a Japanese collector for a sum reported to be in excess of $40 million.

Wyeth isn't the first artist to have spent years drawing and painting one model, but no other artist has ever been so closely scrutinized for doing so.

Although the connection was overlooked at the time in the furious media scramble for scandal, Wyeth's relationship with Helga Testorff affirmed two long-standing interests -painting the human figure, which by itself made him unusual among contemporary artists, and a fascination with German-Prussian culture, which he said he acquired from his maternal grandmother.

Another German immigrant, Chadds Ford farmer Karl Kuerner, inspired Wyeth to create an extended body of paintings and watercolors. Some were portraits, but many were typical of Wyeth in the way they focused on a building, a view out a window or the landsdcape.

Throughout his career, Wyeth sought to reveal the uncommon or the unobserved in the ordinary. He looked for the ominous, or even the horrible, among the benign. In this regard, his work recalls the symbolists, active in Europe in the late 19th century, who created images designed not to describe but to stimulate emotions.

Wyeth's unusual childhood would certainly have reinforced any natural proclivity to interpret the world through his imagination. Even though he had four siblings, Wyeth seems to have grown up as a solitary child who enjoyed a fairytale childhood.

Andrew Newell Wyeth was born in Chadds Ford on July 12, 1917, the son of the noted illustrator Newell Convers Wyeth and Carolyn Brenneman Bockius Wyeth. The youngest of their five children, he had been preceded, in order of age, by Henriette, Carolyn, Nathaniel and Ann.

Henriette and Carolyn also became painters and married artists (Peter Hurd and John McCoy, respectively), and Ann became a composer; Nathaniel, who died recently, is an engineer and inventor.

N.C. Wyeth, as he was known, had moved to the Brandywine Valley to study illustration with Howard Pyle. He eventually became just as famous, particularly for illustrating literary classics like Treasure Island and The Last of the Mohicans.

N.C. encouraged his children to observe the world around them closely and to indulge their imaginations, which they often did by dressing up in the costumes he kept in his studio. "It was the most imaginative, rich childhood you could ever want," Wyeth recalled. "That's why I have so much inside of me that I want to paint."

Because of chronic sinus problems, Wyeth didn't attend public school, but was educated at home by tutors. With his father constantly around as a role model, he began to draw as a young child. He was a natural talent, and by the age of 15, when N.C. formally took him into his studio as a student, he was already an accomplished draftsman.

The apprenticeship, which ended when Wyeth was 17, was his only formal instruction. As he once observed: "I feel that I became an artist out of the life that I led, things that appealed to me and really excited me, and then I began to paint."

When he left his father's tutelage, he was working mainly in watercolor; his first two exhibitions, at the Philadelphia Art Alliance in 1936 and at the Macbeth Gallery in New York City the following year, were entirely in that medium. He was an immediate success; his New York show sold out by the end of the second day.

Watercolor remained a primary medium throughout his career. In the late 1930s his brother-in-law, Peter Hurd, taught him to paint in egg tempera, which until the 15th century was the commonest medium for easel pictures. It's a demanding medium; the pigments, mixed with egg yolk thinned with water, dry quickly, so reworking is difficult.

An artist who uses this technique uses small brushes to make tiny strokes, which results in a smooth, seamless picture surface. This suited him perfectly; as he once explained, "My aim is to escape from the medium with which I work, to leave no residue of technical mannerism to stand between my expression and the observer."

Despite his intention, Wyeth's clean, precise style, complemented by a subdued earth-tone palette, became as distinctive as his fingerprints. It also inspired a host of followers, particularly among watercolorists.

The Wyeth family began to summer in Maine in 1927, at Port Clyde on the west side of Penobscot Bay. On his 22nd in 1939, he met Betsy Merle James, the daughter of a newspaper editor. They were married on May 15, 1940, and subsequently had two sons, Nicholas, an art dealer, and James, known as Jamie, who also is a well-known painter.

Betsy Wyeth has helped her husband to manage his career for more than a half century. It was she to introduced him to the late Christina Olson, the woman portrayed in Christina's World and, like Karl Kuerner, one of Wyeth's favorite subjects.

By the age of 25, Wyeth was recognized as a talented fine artist, an ambition that his father would never fulfill. But at 28 his world crumbled when his father, who had been his professional and spiritual anchor, was killed in an accident.

On Oct. 19, 1945, N.C. was riding with his young grandson, Newell, when his car stalled on a railroad crossing and was struck by a train. "When he died, I was just a clever watercolorist -lots of swish and swash," Andrew told Life magazine writer Richard Meryman in 1965. After the accident, he resolved to honor his father's memory by "doing something serious" with his career.

"I had always had this great motion toward the landscape, and so, with his death . . . the landscape took on a meaning, the quality of him," he told Meryman.

The following year, Wyeth completed Winter 1946, a painting that, like Christina's World, has become one of his signature images. The picture, which shows a boy running down a hill, was a catharsis, for it allowed him to work out the remorse he felt for never having painting his father's portrait.

"The hill finally became a portrait of him," he said in the Life interview. The crossing where N.C. had been killed was just on the other side of the hill.

From that time forward, Wyeth's art became identified equally with the Brandywine Valley around Chadds Ford and with Maine. The Wyeths divided each year between the two places. Their homestead in Chadds Ford consists of an 18th-century miller's house, a gristmill converted to a studio and a granary used as an office. In Cushing, just west of Port Clyde on the Maine coast, they have a restored 18th-century clapboard house. They also own a small island off the coast.

For Wyeth, the Pennsylvania countryside meant solid stone walls and soggy, rich earth; by contrast, Maine seemed to him "all dry bones and desiccated sinews." But Maine also appealed to him because it represented a simplicity that he believed was disappearing elsewhere in America.

Although Wyeth was a famous artist for years, his friends and neighbors in each place shielded him from tourists and the idly curious who hoped to drop into his studio or find him painting outdoors. Anyone who made casual inquiries about Wyeth was likely to be put off with protestations of ignorance about his whereabouts or vague directions that led nowhere in particular.

Some of these friends and neighbors have become famous themselves because of Wyeth. Christina Olson was a crippled woman who lived with her brother, Alvaro, in a weather-beaten house on a coastal promontory. Wyeth painted her and their house many times; for him, her pride, quiet courage and independent spirit epitomized what he loved about the state.

Another Maine neighbor, a teenaged Finnish girl named Siri Erickson, became the subject of his first nudes, beginning in 1969. Where Christina Olson had symbolized deterioration, Siri represented the invigoration and power of youth.

Ralph Cline, a 71-year-old Maine lumberman whom Wyeth has observed marching in a Memorial Day parade, became The Patriot. Wyeth painted him in a bemedaled World War I uniform. One of his most striking images depicts another Maine friend, Walt Anderson, lying in a dory that seems adrift on the sea. Anderson looks like a modern-day Viking being buried at sea.

Wyeth didn't begin to concentrate on painting people under after his father died. In Chadds Ford, his principal subject was Karl Kuerner, the former German army machine-gunner who had become a Pennsylvania dairy farmer. Wyeth had known the Kuerner farm since childhood, and some observers have speculated that Kuerner, who died in 1979, became a surrogate father.

Wyeth's pictures of Kuerner and his farm add up to a collective portrait that is frequently symbolic in its allusions. For instance, the painting called Ground Hog Day, painted in 1959, is a view taken out a window in Kuerner's kitchen. A plate, cup and saucer, and a knife are set on the table; otherwise the sunlit room is empty.

Through the window, one can see the jagged ends of a cut log, the kind of menacing detail that Wyeth often included in his compositions to avoid what he called "sweetness." Although Kuerner isn't present, Wyeth intended that this picture should suggest his character -spartan, honest, perhaps a bit flinty.

And finally there was Helga Testorf, the buxom secret model who had once worked for Kuerner and then for Wyeth's sister, Carolyn. The Helga pictures comprised Wyeth's last extended body of work, and also his last major museum exhibition. It opened at the National Gallery of Art in 1987, and traveled to six other American museums through 1989.

Wyeth's first solo exhibition in a museum came exactly 30 years after his show at the Philadelphia Art Alliance. The Pennsylvania Academy of the Fine Arts mounted a retrospective in 1966 that traveled to the Baltimore Museum of Art, the Whitney Museum of American Art in New York and the Art Institute of Chicago.

Another retrospective followed in 1970, at the Museum of Fine Arts, Boston, and the Museum of Modern Art, which owns Christina's World, gave him a show in 1971. In 1976, he became the first living American artist to receive a retrospective exhibition at the Metropolitan Museum of Art. The show was called "Two Worlds of Andrew Wyeth: Kuerners and Olsons." His show at the Royal Academy of Arts in London was the first there by a living Ameri can artist.

The Brandywine River Museum in Chadds Ford is often called "the Wyeth museum," even though neither Andrew nor any members of his family have any formal connection with it. But the Brandywine features his work and that of his father; a representative group of Andrew's paintings fill a large gallery in an addition that opened in September, 1984. To mark that occasion, Wyeth put together an exhibition of his own paintings from his own collection.

Nineteen eighty-seven was a banner year for Wyeth; besides the Helga exhibition, "Three Generations of Wyeth Art," which featured work by N.C., Andrew and Jamie, began an American tour after opening to large crowds in Leningrad and Moscow. The show eventually went around to world, to museums in Tokyo, Milan and Cambridge, England.

Wyeth didn't make his first trip to Europe until 1977, when he was inducted into the French Academy of Fine Arts -the only American artist since John Singer Sargent to be so honored. The Soviet Academy of Arts made him an honorary member in 1979, and he became an official member in 1986.

He didn't travel to the Soviet Union in 1987 for the "Three Generations Show," reportedly because a hip replacement done several years earlier made extended plane travel difficult. Aside from his hip, Wyeth's only other serious illness occurred in 1950, when a severe respiratory problem resulted in surgery to remove a lung.

Wyeth was honored twice by American presidents. In 1963, President Kennedy made him the first artist to receive the Presidential Medal of Freedom, and in 1970 President Nixon arranged a private exhibition of his paintings in the White House; he was the first living artist to be so honored.

Wyeth received a host of honors in the last four decades of his life, including 21 honorary degrees. The first came in 1954, from Colby College in Maine. Subsequently he was honored by Harvard University (1955), Swarthmore College (1958), the University of Delaware and Temple University (1964), Princeton University (1965), Lincoln University (1966), Ursinus College (1971), the University of Pennsylvania (1972) and, West Chester University (1984), among others.

He was the youngest person ever elected to the American Academy of Arts and Letters and the National Institute of Arts and Letters (1955), which gave him a gold medal "for preeminence in painting" in 1965, and to the American Academy of Arts and Sciences (1960).

The Pennsylvania Academy of the Fine Arts gave him its Gold Medal of Honor in 1966, when his exhibition opened there, and in 1986 Pennsylvania Gov. Dick Thornburgh, describing him as "a true living treasure," named him the state's Distinguished Artist.