PORTLAND, ME. -- As is their wont, students of American art argue endlessly about who was the greatest early American Modernist painter. There are advocates for such diverse talents as Patrick Henry Bruce, Arthur B. Carles, Charles Demuth, Stanton MacDonald-Wright, Alfred Maurer, Morgan Russell, Charles Sheeler, Joseph Stella, and Max Weber. Most attention is inevitably focused, however, on the formidable foursome sponsored by the great New York gallery impresario, Alfred Stieglitz: Arthur Dove, Marsden Hartley, John Marin, and Georgia O'Keeffe.

For many of us, it seems increasingly clear that the finest and most enduring of these American avant-garde artists was the man from Maine, Marsden Hartley (1877-1943).

Coming of age at a time when the European avant-garde commanded most public attention and patronage in this country, Hartley and his Modernist compatriots sought to define an independent American art stimulated by such writers and philosophers as Emerson, Thoreau, and Whitman, painter Alfred Pinkham Ryder, and others. Relentlessly exploring the U.S. and Europe, Hartley became a key figure in the rise of American Modernism.

A traveling retrospective, "Marsden Hartley: American Modern," organized by the Weisman Art Museum of the University of Minnesota in Minneapolis, bolsters the case for Hartley's importance. Currently in the midst of an extended national tour, the exhibition remains at the Portland Museum of Art through April 26. It then travels to venues in California, Louisiana, Oklahoma, the Parrish Art Museum in Southampton, N.Y. (April 11-June 20, 1999), Tennessee, Florida, Texas, and closes at the Joslyn Art Museum in Omaha, Nebraska (July 8-September 21, 2000).

Assembled by Weisman curator and Hartley scholar Patricia McDonnell, the show features more than 50 works drawn from the largest cache of the artist's output, the Weisman Art Museum's Ione and Hudson Walker collection. Hudson Walker, a Minnesota native who became Hartley's last dealer in New York, gave his Hartley holdings - 61 paintings and 54 works on paper - to the university in his home state.

By just about any measure, Hartley led a troubled, conflicted life. He was a gay man in a society that frowned on homosexuality, an artist drawn to abstraction when such work was largely shunned by the public, a man susceptible to powerful swings of mood and capable of ever-changing artistic styles. "Like a true Modernist," says curator McDonnell, Hartley "ran through the full gamut of options then open to avant-garde painters."

Although he was born in the Pine Tree state and always considered himself a Mainer, Hartley spent years in New York, New Mexico and Europe, constantly searching for inspiration and success, before resettling in his native state around the age of 60. Out of his peripatetic experiences came some of the strongest, most challenging and most memorable paintings of Twentieth Century American art.

The works in the exhibition, supplemented by the catalogue text, suggest how Hartley's dramatic shifts in thinking - often in response to cultural trends of the day - were reflected in changes in his art.

Although his formal education was limited - he never went to college - Hartley read widely, from American writers like Emerson, Thoreau, Whitman and William James to French philosopher Henri Bergson to spiritualist texts. Early in his career he hobnobbed with avante-garde artists on both sides of the Atlantic and was befriended by Modernist titans Gertrude Stein and Stieglitz.

Born in Lewiston, a gritty Maine mill town, of English immigrant parents in 1877, Hartley had a difficult childhood. His mother died when he was eight; four years later his father remarried and moved with his new wife to Ohio, leaving his lonely son with an older sister in Maine. "I lived," Hartley later recalled, "an entirely imaginative life of my own."

After he joined his father and sisters in Cleveland in 1893, the young man started taking art lessons. Around the turn of the century he studied at what is now the Cleveland Institute of Art and then at the New York School of Art and National Academy of Design in Manhattan. He spent most summers in Maine. At the age of 29 he changed his first name from Edmund to Marsden, his stepmother's maiden name.

Around 1907 Hartley began serious painting of Maine landscapes, particularly mountains. Two years later he gained attention when Stieglitz featured these early Maine canvases in the artist's first one-person exhibition, at the pioneering 291 Gallery on Fifth Avenue. In that hotbed of international avant-garde art Hartley was exposed to the bright colors of Fauvism and new styles of painting, and was launched into art-world prominence.

Displayed in the exhibition are good examples of Hartley's daring early work, views of Maine scenery executed in the bold strokes of pure color that Stieglitz admired. They represented, said the painter, his "efforts at rendering the God-spirit in the mountains."

Most memorably, "Maine Snowstorm" (1909), a wonderfully blurry blend of whites and pale blues and greens, conveys the snowy ambience of New England winter in a manner reminiscent of Connecticut's John Twachtman, albeit with much more forceful brushwork and heavier impasto. Reflecting the influence of Emerson and Transcendentalism, these early pictures imply the presence of the divine spirit in all of nature's manifestations.

In New York, Hartley's exposure to the Stieglitz circle - notably Dove, Marin and O'Keeffe - and Modernists from Europe such as Matisse and Picasso, stimulated experiments in avant-garde compositions. "Abstraction" of 1911 shows Hartley's explorations of approaches along the lines of his colleagues Dove and Marin, while his strong "Still Life: Fruit" (1911) indicates he was paying close attention to Cezanne's orderly canvases.

The bond between the shy, insecure Hartley and the magnetic, assertive Stieglitz was close and long-lasting. As late as 1926, Stieglitz could boast that "Hartley, like Marin and Dove and O'Keeffe, is one of my babies." Their relations became strained later. In 1939 Hudson Walker became Hartley's dealer.

In 1912 Hartley realized his ambition to visit Europe, where he stayed for three and a half years, first in Paris and then in Berlin. In Paris his heightened interest in Cezanne was reflected in splendid still lifes such as "Still Life" (1912) and others, with tilted tabletops, simple objects, decorative patterns, and a muted palette.

In Europe, Hartley's inclinations toward mysticism were increased by reading the writings and viewing the art of Russian expatriate Wassily Kandinsky, whom he met in Berlin.

Hartley soon came into the Parisian orbit of Gertrude Stein, who welcomed him into her salon of progressive writers and artists and praised his work. "[A]t last," she said of Hartley, "an original American."

Stein's enthusiasm for his work not only encouraged the artist but gave him standing in the City of Light. "The best asset I have...over here is Gertrude Stein," he wrote Stieglitz in 1913. Hartley and Stein also shared an interest in the writings of William James, which led him to readings in European spiritualist works, and encouraged forays into non-objective art. "Abstraction with Flowers" of 1913 is an example of this style.

Hartley continued to sort through a variety of artistic challenges when he relocated to Berlin in 1913. In the German capital on the eve of World War I he created some of the most significant work of his career.

The American traveler developed a real "passion" for Berlin, which he found to be a thoroughly modern, orderly, and clean city. He delighted in the military pomp and pageantry of imperial Germany, with its frequent parades, drills of men in uniform, and other demonstrations of masculine strength and discipline.

Berlin was well-known at this time for its relaxed attitude toward homosexuality. To Hartley it seemed filled with appealing, blond young men in uniform. He developed an intimate friendship with a handsome young Prussian officer, Karl von Freyburg.

Hartley's early Berlin paintings, in a style he called "cosmic Cubism," such as "The Warriors" (1913), blending vivid colors, numbers, military insignia and parade motifs, suggest his excitement at the lively martial spectacle swirling around him. Boldly personal, they also combined Kandinsky's improvisations with the brilliant colors of Franz Marc and other German Expressionists.

Hartley's exuberance dimmed after war was declared in August 1914. Within a few months his dear friend, Lieutenant von Freyburg, died on the Western Front and other acquaintances were killed or wounded in combat. His art took on a less celebratory tone in a series of paintings that were both memorials to his slain companion and tributes to the masses of war dead.

In late 1915 Hartley returned to New York, where anti-German sentiment was running high. The following spring his Berlin works received a generally chilly response when displayed at Stieglitz's gallery. Hartley's imagery, complained leading critic Henry McGride, reflected "all the pomp and circumstance of war." Stieglitz's wife, O'Keeffe, on the other hand, thought the work was "like a brass band in a small closet."

Despondent about criticism of what he thought constituted his best work to date, Hartley reassessed his situation. Concluding that the war had fomented a distrust of artistic experimentation, he decided he needed, as McDonnell puts it, to "redefine himself as an artist."

Before he began the swing from pre-1916 faith in subjectivity to post-1917 belief in objectivity, he painted "One Portrait of One Woman" (1916), which incorporated the bold colors and symbolic motifs of his German work in a somewhat enigmatic homage to Gertrude Stein.

Depressed by America's entry into the war in 1917, Hartley sought relief in a sojourn in New Mexico, at the invitation of Manhattan patron Mabel Dodge, who had relocated to Taos. In that wide open, Southwestern terrain, the Yankee artist became reacquainted with the American landscape. "I am the American rediscovering America," he wrote in a 1918 essay. "America as landscape is profoundly stirring," he added, promoting the idea that native painters should have "firsthand contact with it."

He recorded the arroyos and sweeping vistas of New Mexico in a series of subtly-shaded, lovely pastels and paintings. "I am bewitched by...[the] magnificence and austerity" of the landscape, he declared. "It is the only place in America where true color exists." With pastels such as "New Mexico" (1918) and oils like "Western Flame" (1920), he began to work in what he described as "a sturdier kind of realism...that shall approach the solidity of landscape itself."

For a time, seeking to be as "American" as possible, he became, as McDonnell puts it, "resolutely objective" in his work. The bold, forcefully painted still lifes of the 1920s, such as "Still Life" (1923) and "Fleurs D'Orphee" (1928), suggest his rational approach to painting during this period.

By the 1930s he had softened the "scientific objectivity" of his work, introducing greater personal feelings into his artistic vocabulary. In some of his most compelling images to date, he depicted the massive boulders he observed on the Dogtown Common near Gloucester, Mass. (Similar still lifes and landscapes from the Dogtown period were recently on sale at the Art Dealers Association of America Art Show, reported in the March 13 issue, for prices ranging from $165,000 to $225,000.) A winter sojourn in the Bavarian Alps resulted in several Cezanne-like pastels of the mountainous terrain around Carmisch-Partenkirchen.

The most personal work of this period, "Eight Bells: Memorial to Hart Crane" (1933), filled with symbolic numbers and shapes, constitutes a powerful tribute to his friend, the poet Crane, who had committed suicide. It is a vibrant, memorable image, Ryderesque in its blocky forms.

After more overseas wanderings in the 1930s, Hartley finally returned to the state of his birth in 1937. That first summer he stayed with the widow/muse of sculptor Gaston Lachaise in Georgetown, on the coast near Bath, where he was inspired by the rocky seaside. In Maine, the tentative subjectivity of recent years was replaced by a more pronounced, assured manner.

The return of the native to the Pine Tree state coincided with heightened national interest in regional art. Declaring himself "the painter from Maine," he set out to depict aspects of the state's scenery in idiosyncratic, intensely emotional paintings. "I returned to my tall timbers and my granite cliffs," Hartley said in 1938, "because in them rests the kind of integrity I believe in and from which source I draw my private strength both spiritually and esthetically."

While few of the powerful paintings of Maine are included in the current exhibition - they are prized possessions of other museums all over the country - there are highly evocative works on paper of Maine and several potent portraits of the rugged folk of nearby Nova Scotia for whom Hartley developed a deep affection.

While staying with the Masons, a family of intrepid fishermen in Nova Scotia, the painter came face to face with the dangers and hardships confronting these men of the sea on a daily basis. He also experienced additional abrupt deaths, continuing his life-long pattern of loss and isolation. Hartley was devastated by the drowning deaths of two of the Mason sons, particularly Alty Mason, to whom he had become closely attached.

Other paintings of fishermen following Alty Mason's drowning, infused with images of Christian martyrdom, were executed in a direct, almost primitive manner. "Nova Scotia Fishermen" (1938), a compelling oil painted after he returned to Maine, disconsolate and ill, sold at Sotheby's last December for $745,000.

The Maine drawings on view lack the craggy power of his late oils, but they do convey his innate feel for the state's rockbound landscape and his sensitivity to the rhythms of local life. Hartley was particularly drawn to towering Mount Katahdin, which he depicted in several impressive paintings. "I know I have seen God now," he declared after climbing up the mountain. "Mount Katahdin" (1940-41), a black crayon sketch, captures some of the drama and skyward thrust of that Maine landmark.

Perhaps the most powerful works of Hartley's entire career are his final seascapes. They are boldly stroked, highly simplified images of timeless beauty and potency. As the great art historian Oliver Larkin observed, in "Hartley's splendid last five years...thanks to his friend Hudson Walker, Americans rediscovered a painter-poet whose imagination could match Ryder's and whose waves moved with the power of Winslow Homer's."

Before he had time to move onto even greater heights, Hartley died in Ellsworth, Me., in 1943. He was 66 years old.

In 1993 critic Robert Hughes wrote that "Marsden Hartley is tremendously important." By placing his art in the context of his times, this exhibition underscores that importance and sheds new light on one of America's master artists.

The fully-illustrated exhibition catalogue, written by curator McDonnell, stresses Hartley's shifting artistic practices and beliefs in the context of the turbulent times through which he lived. The text is supplemented with a helpful chronology.

One interesting nugget in the catalogue: while Hughes in his recent book, American Visions, declares that "no photo of von Freyburg [Hartley's Berlin love] has survived," McDonnell displays on page 37 a 1913 photograph of the handsome German officer on horseback. The photograph is from the Beinecke Rare Book and Manuscript Library, Yale University.

The Portland Museum of Art is at Seven Congress Square, Portland, Me. Telephone 207/775-6148.