"At 20, in Paris," wrote the French-born sculptor Gaston Lachaise (1882-1935), "I met a young American person who immediately became the primary inspiration which awakened my vision . . . Throughout my career, as an artist, I refer to this person by the word 'Woman.' "

Her name was Isabel Nagle, and she was a woman all right, as anyone who has seen Lachaise's grand, heroically proportioned sculptural paeans to her ample form will attest. She was 10 years older than Lachaise, and a Bostonian wife and mother unwilling to divorce until her son had graduated Harvard. Always unstoppable in romance, Lachaise followed her back to America, and 15 years later, when she was 45, made her his wife.

He obviously saw a good deal of her in the interim: to this day anyone who thinks about Lachaise thinks first of the life-sized, idealized nude sculptures of Isabel, his "eternal female" and artistic emblem. But there is another realm of Lachaise's oeuvre that never has been properly seen, examined or assessed: his portraiture. "Gaston Lachaise: Portrait Sculpture," which opened yesterday at the National Portrait Gallery, not only does a fine job of filling that gap but also leaves the distinct impression that Lachaise deserves more respect than he has had.

Many Americans still think of him as French, but Lachaise became an American citizen in 1916 while working for sculptor Paul Manship in New York, and spent the rest of his life in that city and at his summer home in Georgetown, Maine. The son of a French cabinetmaker and woodcarver, Lachaise had shown exceptional talent as a portraitist during his student days in Paris, when a bust of his sister was shown at the 1899 Salon of the Societe des Artistes Franc,ais even though, at 17, he was underage. Lachaise was still making portraits until three days before his sudden death at age 52. Such portrait commissions were obviously a major source of income throughout his life.

All but two of his known heads, busts and full-length portraits -- some 60 in all -- are in this exhibition. Yet the show is not only about portraiture. It is also about the life and struggle of a gifted, well-connected immigrant artist in New York in the '20s and '30s, when his friends, subjects and patrons included the leading lights of the young literary and artistic avant-garde, among them e.e. cummings, Marianne Moore, Alfred Stieglitz, Georgia O'Keeffe and Lincoln Kirstein, to name but a few. This show brings that milieu to life -- the very thing that portrait galleries are meant to do.

The show begins with portrait variations inspired by zaftig Isabel: heads, busts and small full-length statuettes that go well beyond portaiture to explore pure sculptural form. There are also five telling variations on Marie Pierce, Isabel's niece, that illustrate Lachaise's working method and impulse toward simplification and abstraction. He starts with a straightforward, detailed head with masses of bobbed hair, then changes the tilt of the head, elongates the neck and ultimately removes the hair as he plays with pure form; the result is a masklike effect. The final version in nickel-plated bronze has the highly reflective, machine-made look of the Art Deco period, with which Lachaise was much in tune. Here, as in all of his best portraits, he has moved from a specific image to a timeless one.

Next comes the encounter with the extraordinarily creative circle surrounding The Dial, an avant-garde literary and arts magazine taken over in 1919 by Schofield Thayer and James Sibley Watson Jr., Harvard classmates of Isabel's only son Edward Nagel, who introduced Lachaise into the group. The magazine, which provided what art critic Henry McBride called "a continual pounding on the desk for its prote'ge's," took Lachaise to its bosom. Writers and editors repeatedly reproduced and wrote about his work, and many of those who could afford it (as well as some who couldn't) commissioned portraits of themselves and their families.

The show is filled with them: the spectacular, bovine face of Carl Van Vechten; the troubled (and ultimately institutionalized) son, Nagel; composer Edgard Varese; critic McBride; and Gilbert Seldes, who not only wrote a profile of Lachaise for The New Yorker, but also commissioned portraits of his entire family.

There are others as well: among the best, the intense, craggy-faced painter John Marin, and the formidable dealer-photographer Alfred Stieglitz, who gave Lachaise a show in 1927, introducing him to important collectors, including Duncan Phillips. One senses Stieglitz's power over the artist not only in the cubistic bronze portrait of him, but also in the white-marble carving of his wife, painter Georgia O'Keeffe, portrayed in a rather prim and saccharine way. One suspects a fear of displeasing Stieglitz, or perhaps the stony lady, put Lachaise off.

The last of the three galleries includes the latest works, among them a full-scale standing male nude, rigid and classical and passionless. "I do not love the male as I love the female," he wrote to Isabel in Maine, and that is clear. But there is one exceptional male nude: the "Walking Man," which is, in fact, a portrait of Lincoln Kirstein, founder of the New York City Ballet and great champion of the avant-garde. The beetle-browed Kirstein is here shown with his close-cropped head exaggerated into a dome to suggest the look of an Egyptian pharaoh and to imply his extraordinary mental capacity. The simple gesture of the pointed toe identifies him with his great passion, the ballet.

This and the small bronze portrait of Isabel titled "Walking Woman" are among the finest works in the show, and underscore that it was in the full-length portraits -- whether large or small -- that Lachaise made his most distinctive contribution.

In fact, apart from the stunning life-size figure of Isabel that serves as the centerpiece of this show, all of the best figure portraits here are under 25 inches, proving that monumentality, at least for Lachaise, was not a function of size. Tabletop portraits of Isabel striding, slumping in a chair or standing with her hands on her hips are in every way as formidable and voluptuous as the larger nudes.

One begins to wonder, after a while, about Lachaise's romantic obsession with Isabel, who seems to have been monumentally self-centered as well as self-possessed (to put it kindly), and who always spent money faster than Lachaise could earn it. She had a cook, and evidently ran up outrageous grocery bills, something Kirstein reprimanded her for after the artist's death. Lachaise sometimes bartered his talents to please her: of a deal struck with her dressmaker, Mme. Georgette Ouzounoff, Lachaise wrote to Isabel, who was again in Maine, "She could make you a gown equivalent to the price of a statuette they want."

Later, as he was creating the splendid draped figure on display here, he wrote, "She is not as beautiful as you but all the same a beautiful thing." He was never objective where Isabel was concerned.

After the artist's sudden death in 1935 -- reportedly from an infection following the extraction of a tooth -- Henry McBride wrote: "A few of us who knew that Gaston Lachaise was great sat there like wooden images in a Eugene O'Neill play . . . to ruminate on the nature of greatness in America . . . and its recompense."

It is hard to believe that Lachaise was not appreciated in his lifetime, given the evidence advanced in this show. But opinions of his work, outside the Dial circle, seem to have varied widely, and though he was given his first museum show at the Museum of Modern Art -- something that Kirstein had fought for -- six months before his death, nothing in that exhibition was sold.

Since then, Lachaise has been remembered for his standing nudes, but he has remained a marginal figure and opinions on his work have continued to vary. Of his 1964 retrospective at the Whitney Museum, the New York Times critic, the late John Canaday, said, "it is embarrassing where it is not appalling," while Emily Genauer, in The New York Herald Tribune, wrote that Lachaise "rose to heights no other American sculptor has touched." Surely Genauer was closer to the truth, though one hesitates to jump on her bandwagon without benefit of an updated retrospective. Tastes change.

In the end, Lachaise was a personal and idiosyncratic artist, defying classification in an art world that has required, at least in this century, that an artist change the course of art history to really count. Lachaise did not change the course of American art history, but he amply graced it. And as this exhibition proves, any future study of American portraiture will have to take him seriously into account.

A comprehensive catalogue illustrating each of Lachaise's known portraits has been published, and makes fascinating reading for anyone interested in the New York intellectual milieu of the '20s and '30s. Both the catalogue and exhibition, which continues through Feb. 15, have been supported by the Lachaise Foundation.