From 1953 until 1969, when she died at age 62, Martha Jackson operated one of the more sophisticated art dealerships in Manhattan.

In the brownstone gallery on East 66th Street or, after 1955, on East 69th, one was as likely to come upon works by outstanding Europeans -- Francis Bacon, Barbara Hepworth, Antoni Tapies, Karel Appel, Marino Marini -- as by preeminent Americans of the New York School -- Willem de Kooning, Hans Hofmann, Adolph Gottlieb. One would have seen works by older or dead Americans -- Milton Avery, Alexander Calder, Arshile Gorky, Marsden Hartley -- alongside those by lesser-known New Yorkers -- Lawrence Calcagno, John Hultberg, Lee Krasner, Paul Jenkins, Norman Bluhm.

Without making much apparent fuss about it, she supported and displayed works by female artists -- Krasner, Marisol (Escobar), Grace Hartigan -- at a time when this was not the rule. And she kept her eyes open for non-New York artists whose work intrigued her -- Washingtonians Morris Louis during the 1950s and Ed McGowin in the 1960s, among others.

Her taste was unusually broad. Though no traditionalist, she maintained faith in the power of representation and figuration in art -- Hultberg, Hartigan, Lester Johnson, Bob Thompson -- when abstraction was the dernier cri. Nor did she allow her taste to stultify: She was responsive to Pop art, selected the first Op art show in the United States, and maintained a lasting business relationship with Julian Stanczak, one of its best practitioners.

It almost goes without saying, then, that an exhibition devoted to the memory of Martha Jackson would be an interesting, and possibly even a triumphant, affair. "The Martha Jackson Memorial Collection," an exhibition that opened yesterday at the National Museum of American Art of about half of the 127 paintings and sculptures donated five years ago to the museum by her son David Anderson, is a bit of both.

The show does not encapsulate the cosmopolitanism of her operation (non-Americans are excluded), nor does it encompass the across-the-generations breadth of her activities, nor does it touch upon some of the more notable high points of her career. She exhibited important canvases by de Kooning during the 1950s, for instance, but there are no de Koonings in the gift or the show.

But what the show does, it does very well. By focusing on the works of so-called "second-generation" New York School painters, artists whose double-edged inheritance was to follow the insights of "the new American painting" and to expand upon them, the exhibit rekindles our appreciation of the breadth of avant-garde painting in New York during the 1950s.

The stars of this show -- Hultberg, Hartigan, Thompson, Johnson and Bluhm -- are not customarily given top billing in any review of the period. This is fair. Their collective achievements do not quite match those of such generative forces as Jackson Pollock or Mark Rothko or de Kooning. Even so, it is a great pleasure to see in some depth how good these artists, and others in the show, actually were.

Bluhm is an excellent example of a vastly undervalued talent. His best painting here, a wall-spanning triptych titled "Acheron," was painted in 1971. This would seem to take it out of the relevant time frame, and yet with its swirling loops of creamy color, its splashes of paint, its sure-fire manipulations of space, it is a gestural painting of resplendent beauty and improbable authority. Scant wonder that Bluhm went in for classic titles with tragic implications (Acheron, curator Harry Rand tells us in the catalogue, derives from the Greek root for affliction), for he was practicing at the highest level a kind of painting that had long been out of fashion. Consequently, his achievement went largely unnoticed.

Simply to see this magnificent work is to question the kind of canned history -- Progress in Art -- in which the authenticity of a style is cut off, arbitrarily, at a certain date. A similar painting in this show is "Sunflower III" by Joan Mitchell, a ravishing, luminous patchwork of rough but somehow elegant marks of the brush that appropriate lessons learned from de Kooning and the late Monet with complete self-confidence. It was painted in 1969.

The seven paintings by Hultberg, dating from 1954 to 1974, comprise a sort of mini-retrospective. It is a fascinating body of work -- again out of sync with fashion -- in which we witness the gradual emergence of a shadowy, gloomy urban world of deep exterior or interior spaces from the flickering flat surfaces of the early pieces. Hultberg seems intent on turning the exultant romantic concept of the sublime inside out, and in unsettling but beautiful paintings such as the huge "Giant" (1963), he thoroughly succeeds.

Although very different in esthetic approach, Johnson's figurative paintings have something of the same memorable, somber impact. Johnson is at once a classicist (he prefers frontal, archetypal figures), a primitivist (the figures possess a totemic force), and a Modernist (he knows, and uses, Matisse and Rothko, among others).

Thompson, who died at age 29 in 1966, is perhaps the most idiosyncratic of this individualistic group. Stylized and brilliantly colored, the other-worldly human figures, demons, saints and angels that disport themselves across the surfaces of his paintings are at once serene and unhinging. By contrast, the fragmentary figures and their accouterments in Hartigan's big, strong, patterned canvases, "Modern Cycle" (1967) and "Inclement Weather" (1970), seem almost playfully anchored in the here and now.

There are many other points of interest in this exhibition: Michael Goldberg's "Sardines" (1955), with its quintessential mid-'50s New York School look (Frank O'Hara wrote a poem, "Why I Am Not a Painter," about this work); the elongated woman in Eldzier Cortor's "Southern Gate" (1942-43), at once dreamy and sensual; Marisol's "President Charles DeGaulle" (1967), a superb sculptural spoof; Alex Katz's sets for Kenneth Koch's 1962 play, "George Washington Crossing the Delaware"; several early works on paper by Sam Francis; and exemplary works by Calcagno, Stanczak, James Brooks, Frank Lobdell and others.

Martha Jackson, born to wealth in Buffalo in 1907, was married twice and lived conventionally until she decisively altered her life by moving to New York and enrolling in the Hans Hofmann School of Art in 1949. Already she was a significant collector; Hofmann encouraged her to become a dealer. Despite her late start she was a great success, a fully engaged professional who was not afraid to take risks (she sold many a painting from her own collection to support the gallery's involvement in contemporary art) or to trust her own educated eye.

Rand, who selected the show from Anderson's gift, took pains to seek out telling reminiscences from the artists for his catalogue essay. He closes it on an elegiac note, recalling a time "when artists' careers were marked by a slower, more deliberate trajectory, when dealers played a more relaxed and personal role intervening between a customer's delighted wonder and the artist's yearning for recognition and sales."

Although the donation was made in 1980, only a few of the works have been displayed at the museum before now. The exhibit thus provides an overview of a significant addition to the collection of the National Museum of American Art, a time-warp revelation and a fitting tribute to Jackson. It continues through September 15.