John La Farge -- easel painter, watercolorist, illustrator, muralist, decorator, critic, world traveler, conversationalist -- was an impressive man and a major figure in late 19th-century American art. But he cannot be judged a major artist.

His gifts, though not inconsequential, were limited and spread thinly. He created beautiful and moving images and objects but, with one large exception, only episodically. He was at times an adventurous artist and his work opened new paths, but his sensibility at heart remained conventional. Though not a mere dabbler -- far from it -- he often failed to push his insights to the limit.

All of this, and more, is evident in the retrospective of La Farge's work opening today at the National Museum of American Art. It's a fascinating show. La Farge was at once a cosmopolitan, a traditionalist, a romantic and an innovator; his very breadth ensures that the show touches upon many aspects of American culture of his time.

And his best work -- the early still life paintings, a few striking watercolors, here and there an evocative landscape or figure painting, and the altogether splendid stained glass pieces -- is very much worth seeing for its own sake.

The show begins and ends with his stained-glass works, and though this seems fitting -- we can see now that they were his principal sustained achievement -- it also is somewhat ironic. It is only today, because the buildings for which these windows were designed have been demolished, that we can appreciate them as individual "paintings with colored light," as they are aptly characterized in the catalogue.

La Farge was born in New York City in 1835, the first child of wealthy French e'migre's. His upbringing -- Roman Catholic, strongly European, cultured and refined -- helps to explain something of the cultural ambivalence of his art. Henri Focillon, after visiting a retrospective of La Farge's work in 1936, said that "to the French traveler, attentive guest of the United States, it seemed almost as if one caught the whisperings of a dual language, that of America and that of his own country."

In his early twenties La Farge had experienced the requisite grand tour of Europe; he had even studied painting for a brief while in Paris in the studio of Thomas Couture. But he did not decide in earnest to become a painter until 1859, the year he moved to Newport, R.I., to join the small, highly cultivated artists' colony there.

His progress was notable. There are two paintings from 1859 in the show, one a fairly conventional still life exercise, the other a study of two water lilies in a simple white bowl that adumbrates the remarkable series of still lifes he turned out in the early 1860s. A wall holding four of these paintings -- flowers arranged in bowls or in wreaths and played against subtle white backgrounds -- is most instructive and very moving.

There is nothing quite like these paintings in the preceding decades of American art. There is no hardness in them, no clarity -- highly emotive suggestion here replaces physical definition. Even though we can identify the varieties of blossom in these shaded works, it is the exquisite mood, the reverie that counts. The same can be said for a few of the moody landscape studies from this period (most notably "Snow Storm" of 1865).

La Farge here was demonstrating for the first time the start-and-stop pattern of his career -- his remarkable capacity to learn from fresh sources, to foreshadow major artistic developments and then, suddenly, to abandon one line of thought for another. In their subtle shadings and tactile brushwork these works stand with advanced contemporary French painting, and in their radically simplified compositions they resemble Japanese woodblock prints. La Farge was the first American artist successfully to absorb these influences, but he did not for long explore them in oil painting. Similarly, though he broke new ground with a series of extremely imaginative magazine and book illustrations in the 1860s, he dropped this field entirely.

In the 1870s La Farge began to pursue what he conceived of as the greater artistic goal of figurative, allegorical painting. The unevenness of the results can be clearly seen here. As a draftsman La Farge never fully mastered the human figure, but because he was a superior colorist he was able to make a few haunting figurative works -- "The Golden Age" (1878-79), with its dreamy, solitary female figure, is a symbolist picture created before the invention of symbolism as a school. By contrast "The Three Wise Men" (1878-79), though truly Venetian in color, is pathetically weak in composition.

His greatest achievement as a muralist -- the decoration of the interior of Henry Hobson Richardson's great Trinity Church in Boston -- cannot adequately be represented in a museum show. Here, too, his art was predictive and the results mixed: He and Richardson can be given credit for launching the American Renaissance mural movement, but it is also clear that La Farge's chasing after the muralist's muse was distracting. He was not really an artist equipped to make the major, moralizing statement.

His great triumph, other than the occasional lambent watercolor interspersed among fussy ones, was in stained glass. Here alone did he seize the initiative and maintain it. As Henry A. La Farge, the painter's grandson, pointed out in his catalogue essay, when La Farge began to work with stained glass in 1875 "he found that almost nothing was left of that tradition and that practically no glass of good quality was available in this country for making windows." La Farge changed that situation dramatically in the next two decades and, in the process, greatly expanded the possibilities of the ancient medium.

La Farge's technical innovations were many. The most important was his introduction of opalescent glass, which, because of its intrinsic colors, made it possible, as scholar Henry Adams states in the catalogue, "to manipulate effects of color not by painting on glass but by exploiting the properties of glass itself." And by no means did he stop there.

None of his windows is exactly like another. In each he experimented aggressively -- each is a little encyclopedia of technical innovations, of panels set in triple, quadruple and even quintuple layers, of colors and shadows new to the medium, of thickly molded pieces and thin, transparent ones. Each is an impressively sculptural object and most are genuinely inventive compositions. Here, too, La Farge applied lessons learned from Japanese art, and he obviously looked at Islamic sources, but his decorative sense was his own.

The catalogue, handsomely produced by Abbeville Press and containing essays on most facets of La Farge's art, also contributes to our knowledge of the man. His was a commanding personality that exercised a spell upon fellow artists but also, astonishingly, upon two great writers -- Henry James, of whom there is an affecting portrait in the show, and Henry Adams, with whom La Farge traveled to Japan and to the South Pacific islands.

The exhibition continues through Oct. 12.