Art thrives in paradox. It requires a stable, prosperous environment, but also needs the ferment of new ideas, new attitudes jostling each other and the old ones.
New York City at the beginning of this century was a paradigm of such conditions, what with the explosion of financial growth, the opening up of office work for women, and the sweatshops filled with Europe's ''huddled masses.'' All of this contributed to the climate that brought four young newspaper illustrators away from the more conservative, static art establishment of Philadelphia to develop their careers as fine artists in New York, which was about to become the defining city of the future.
John Sloan, George Luks, William Glackens, and Everett Shinn were following the urging of their mentor and teacher, Robert Henri, a painter who had studied in France. They were later joined by a younger student of Henri's, George Bellows.
''Go out into the streets and look at life,'' the charismatic Henri exhorted his students. He, himself, however, displayed something of the do-as-I-say-not-as-I-do attitude, because the most conspicuous part of his oeuvre is portraits and character studies. Some of these were, indeed, of ''street kids'' such as the wistful young black ''Willie Gee.''
But still the group heeded him and immersed themselves in the heady mix of changing social mores, immigrant cultures, and an economy whose growth was evident for all to see. The six friends - all very individual - are represented in the exhibition, ''Metropolitan Lives: The Ashcan Artists and Their New York'' at the National Museum of American Art in Washington, D.C. They were derisively dubbed the Ashcan School after their only exhibition together in 1908 at the Macbeth Galleries because of their gritty subject matter. They never constituted even as much of a school of painting as the French Impressionists.
John Sloan's ''Six O'Clock, Winter'' (1912) looks larger than its 26 by 32 inches because of its dramatic, daring composition. The great, dark thrusting mass of the elevated platform with its crowd of humanity pressing to board the train is played against a beautifully modulated blue evening sky. Beneath the train, homeward-bound workers, men and women, cover the immediate foreground. It almost looks as if the artist painted the scene surrounded by the rush-hour throng. This ''street level'' view without the traditional distance between artist and subject was another Ashcan innovation. Sloan notes not only the ''modern'' transport of the elevated system, but also, in the narrow band of light above the pedestrians' heads, a trolley car, an open van being unloaded, and a horse-drawn carriage, all enmeshed in a traffic jam.
There are no ''Els'' (elevated trains) in Manhattan now, although in the 1950s one could still experience their deafening roar overhead while being showered with greasy soot. Some sections of overhead track remain on the subway system, recalling Sloan's masterpiece.
Sloan, Glackens, Shinn, and Luks all continued illustrating for newspapers and magazines in New York while their careers as artists were getting started. Their training in depicting complicated news events made it relatively easy for them to execute intricate panoramas of the city in all its diversity. George Luks seems to have taken more pleasure in the newspaper work than the rest, and became well known when he took over a pioneer cartoon called, ''Hogan's Alley.'' This was a hilarious look at a tenement neighborhood.
All of the artists also zoomed in on vignettes of city folk. Bellows, best known for his prizefighters, painted a moving glimpse of the uncertainties of day laborers on a dock, played against the magnificence of an ocean liner and the distant towers of the city.
Everett Shinn preferred the theater and painted performers and audiences with great panache. Glackens's choice was recreation at beaches and parks, especially festive days in Central Park.
Luks, the painter, kept his eye on everyday pursuits and hardships. Critics compared his paintings to the writings of Charles Dickens and Maxim Gorky.
''Knitting for the Soldiers: High Bridge Park'' (ca. 1918) displays another side of Luks's art - brilliant post-Impressionist coloring and techniques. He had early exposure to European art when he studied briefly in Dusseldorf, Germany. The painting has interesting formal aspects such as the simplified, repeated shapes of the baby carriages defining the spatial arrangement of the figures and the multi-colored bluish shadow in the foreground, echoing the sober blue trees of the background. His figures convey a sense of individuality, although only two of them have distinct facial features.
High Bridge Park was in a middle-class district. The women are not chattering ladies or nannies, but seem to be gathered in quiet neighborliness to make their contribution to the war effort in the winter sunshine. Luks invests them with a sense of seriousness and high purpose about their work.
The New York of the Ashcan Artists had still the companionableness of the American small town. The loneliness and alienation of the big-city dweller was yet to be made manifest.
* ''Metropolitan Lives: The Ashcan Artists and Their New York'' at the National Museum of American Art in Washington, D.C., runs through March 17.