Mary Cassatt--the only American ever invited to exhibit with the French impressionists--was a talented, highborn expatriate artist from Philadelphia who spent her life painting variations on a single theme: the daily activities of the cultured, upper-crust women she knew in Paris.

Talent aside, they were much like her: French or American, they wore hats and gloves while sipping tea from gold-rimmed cups, dressed elegantly for the theater and read quietly in gardens with dogs on their laps.

Their gowns were by Worth or other couturiers, their paintings by Sargent, Whistler, Degas, Monet and Cassatt. And their children--like their city and country houses--were mostly tended by others.

It was only in this respect that her life differed. Choosing the role of artist over wife, Cassatt (1844-1926) had no children, though they were central to her art. She said years later that that was her only regret.

Her women seem old-fashioned today. But they were modern then. Subtle changes in society were afoot, as women began to demand the right to vote, and to educate girls the same as boys. There was even a movement underway urging upper-class mothers to do away with wet nurses and take a more active role in raising their own children.

In her best works, Cassatt focused on the dignity of these women, ennobling their maternal role without sentimentality (though she sometimes slipped). Cassatt gave her subjects a thoughtful intelligence through alert postures and expressive eyes, often riveted on the activity at hand. The best example is a painting of her cultured mother, the subject of her "Portrait of a Lady," in which Katherine Cassatt is shown intently reading the front page of a newspaper.

Cassatt's goal, however, was to paint scenes of contemporary life, not portraits. And she reveled in the textures and patterns of what she saw: a shimmering silver teapot, the flowered upholstery on an overstuffed chair, the fashion plates who occupied the boxes at the new Paris opera. Later, she took similar pleasure in painting the soft skin of a child cuddled in its mother's arms, or the glorious dark eyelashes of her niece playing in the sand.

Cassatt looked intently at her world, and her 65 paintings and color prints at the National Gallery make us do likewise.

This exhibition--a shortened version of the retrospective first shown at the Art Institute of Chicago--sketches out the trajectory of Cassatt's professional career. And it starts with some silly early paintings made during a study trip to Italy and Spain--one of many she made in her youth--involving toreadors and flirtatious ladies in the style of Velazquez.

Though paintings of this sort were apparently accepted into the official Paris salons in the early 1870s, they serve here chiefly to explain why Degas, Monet, Renoir, Pissarro, Morisot and others felt the need to rebel.

Cassatt's work was profoundly changed by the paintings of these rebels, especially Degas, of whom she later said, "The first sight of Degas's pictures was the turning point in my artistic life." He became her mentor and friend, and in 1877 invited her to be part of the next "impressionist" exhibition, the first of several shows that would secure her place as the only American member of the Paris avant-garde.

In 1874, Cassatt settled in Paris for good and began to focus on the arena that she knew best--the fashionable cultural life of the city. Night life of all sorts was booming with the help of better artificial illumination, and the sumptuous new Paris Opera, opened in 1875, had already inspired works by Degas, Renoir and others.

The wealthy--then as now--had regular seats in the mirrored boxes, or loges, which offered ready-made compositions, enhanced by flickering effects from the gas- and limelight, soon to be replaced by electric illumination.

Beaudelaire wrote of this spectacle: "Sometimes in the diffused radiance of opera or theater, young girls of the best society, their shoulders, eyes and jewels catching the light, resemble gorgeous portraits as they sit in their boxes."

The mirrored walls of these boxes--the only place where unaccompanied ladies could sit--added to the luminous visual effects and were taken full advantage of by Cassatt. Like Degas, she often used mirrors to add interest and complexity to these compositions: Paintings that appear to depict two different people often depict only one, plus a reflection of her back. But Cassatt was looking at the women in the audience, not the actors onstage.

There's lots of looking going on in these pictures, as there apparently was at the theater itself. Cassatt makes witty reference to this in "At the Francais" (1871), in which a lady in black afternoon dress and bonnet peers at the stage through opera glasses, while a man in a nearby box peers at her.

By 1881-82, when she painted "Women in Loge"--two young women seemingly aware of being stared at, one with a fan covering part of her face--Cassatt was in full possession of her painterly powers, a master of color and swift, flickering brush strokes. She was also experimenting with different media, using metallic paint to add sparkle to the fan, aquatint to add texture to the black velvet ribbon around one young woman's neck.

By 1882, when she painted her last loge picture, she had begun painting women closer to home, partly of necessity. By then Cassatt's aging parents and her ailing sister, Lydia--with whom she had planned to grow old--had moved in with her in Paris, and Cassatt's increasing involvement with them is reflected in her work. At the time Cassatt also made several paintings of Lydia, who is the guest wearing the bonnet in "Tea" and, finally, in the ominous "Autumn," in which her pale face stands in stark contrast to the autumnal landscape that seems to engulf her.

After Lydia's death in 1882, visits from their brothers and their countless children helped console Cassatt. They also provided models for some of her most endearing works, including "Children on the Shore" (1885) and "Portrait of Alexander J. Cassatt and His Son Robert Kelso Cassatt, 1884-85," her only depiction of paternal affection.

Soon, Cassatt embarked on the theme of mothers and children, which was to occupy her for the next three decades, and for which she is still, unfortunately, best known. The central point made by this show is that Cassatt had a far broader range as an artist than she has ever been given credit for.

This exhibition includes several strong maternity pictures, along with others that go over the line into Renoir-like bathos. But it also includes a gallery devoted to the most remarkable images Cassatt ever made: a suite of 10 color etchings and drypoints with aquatint that she was inspired to create after seeing an exhibition of Japanese woodblock prints in 1890. She wrote ecstatically of that exhibition: "I can think of nothing but color on copper," she told her fellow artist Berthe Morisot. Also concerned with the everyday activities of women, these prints depicted them bathing, dressing, writing letters, combing their hair and hugging their children--all themes that coincided with Cassatt's lifelong interests.

The resulting series of 10 prints shows a mastery of line and composition, and a delicacy of color, that place them among the greatest works Cassatt--or any other printmaker--produced in late-19th-century France. They also include her most exquisite portrayals of mothers and their children, works of a tenderness and empathy rarely approached elsewhere in her work.

Two spectacular paintings from the 1890s, "The Boating Party" and "Ellen Mary Cassatt in a White Coat," also number among the masterpieces here, though they seem oddly out of place amid an otherwise dreary lot of late paintings that hang at the end of this show.

In 1892, Cassatt was commissioned to do a mural on the subject of "Modern Woman" for the Chicago 1893 World's Columbian Exposition, and it seems to have done her work no good. The mural disappeared after the exposition closed, but the metaphoric paintings based on it suggest that this was no great loss. Thereafter, with only a few exceptions, her paintings--including her maternity scenes--descend into stiff, photographic sentimentality. In this context, her greatest painting, "The Boating Party," from 1894, seems to come out of nowhere. Have crucial works been left out of this scaled-back show?

What is clear here is how deeply involved Cassatt's life was with that of her family, and how profoundly their health or illness affected not only her ability to work but also her subject matter. The tragic loss of her sister seems to have given her paintings a new emotional depth. Later she paints her mother once again, old and infirm. All of the vitality of the earlier picture has been replaced by resignation and age. Cassatt said that her mother's death, six years after the painting was completed, left her "so bereft and so tired of life that I thought I could not live."

But then came her American rediscovery in 1898 after a highly successful show at Durand-Ruel's Manhattan gallery. The reaction gave her--if not her art--a new lease on life. It didn't hurt that by then her brother Alexander was president of the Pennsylvania Railroad and one of the richest and most powerful men in the country--a fact no reviewer failed to mention. But Cassatt's pleasure was undiluted. She received 20 portrait commissions in Boston, all of which she completed, mostly in pastel. Unfortunately, no pastels are included in the gallery's version of this show. Perhaps they would have helped to round out the presentation of her work from the '90s.

In 1908, at age 64, Cassatt made her final visit to the United States, mostly to comfort her closest friend, Louisine Havemeyer, collector and suffragette, whose husband had just died. (With Cassatt's help, Havemeyer had acquired 65 works by Degas, along with other masterpieces of impressionism, now in the Metropolitan Museum in New York.) Two years later, after a visit to a show of canvases by Peter Paul Rubens, Cassatt wrote Louisine: "The exhibition as a whole is disappointing. I mean of course . . . we see things differently now--& after all one must be of one's time."

As indeed she was. She took up the cause of women's suffrage and sent 18 works to a New York exhibit supporting it in 1915, before diabetes and cataracts forced her to abandon her art.

After surviving the hardships of World War I, Cassatt died in France in 1926, a chevalier of the Legion of Honor, determined to see that American museums, too, would come to honor her works. And she would be pleased to know that the National Gallery of Art, which didn't exist in her time, has most of the best of them.

MARY CASSATT' AT THE NATIONAL GALLERY

"Mary Cassatt" will be on view in the National Gallery East Building through Sept. 6. No tickets are required. Organized by the Art Institute of Chicago in collaboration with the Museum of Fine Arts, Boston, the show was presented in both those cities before coming here in a scaled-back form. Today from 2 to 4 p.m., Cassatt scholars will give two free lectures in the East Building Auditorium.

The East Building, on the Mall at Fourth Street and Constitution Avenue NW, is open Monday through Saturday from 10 a.m. to 5 p.m. and Sunday from 11 a.m. to 6 p.m. Admission is free. The Washington showing is supported by Aetna Inc. An extensive catalogue with recent scholarship has been published, along with a free brochure. Call 202-789-3030 for information on special tours and free family programs.

CAPTION: "Women in a Loge," one of the works in the National Gallery show.

CAPTION: All in the family: Cassatt's sister Lydia is the woman wearing the bonnet in "Tea," from 1879-80, while "Portrait of a Lady," below, captures the artist's mother intently reading a newspaper in 1878; and the 1885 work "Children on the Shore" features Cassatt's nieces.