Summer in Washington means two things: heat and tourists. If you're stuck in town during the dog days of summer, neither of them can be avoided entirely. One place to cool your heels, though, and dream of that, holiday in France or voyage to Tahiti you'd like to be taking and can't afford is the National Gallery of Art, where "Post-Impressionism: Cross-Currents in European and American Painting, 1880-1906" will be on view through Sept. 1. And if you're worried about hordes of out-of-town visitors blocking your view of Van Gogh and Cezanne, the NGA's summertime hours (through Labor Day: Mon.- Sat. 10 a.m.-9 p.m.; Sun. noon-9 p.m.) should help ease the crowds.

That Washington is seeing the Post-Impressionists is in fact a happy result of an unhappy event: In response to the Soviet invasion of Afghanistan, the NGA canceled the scheduled Russian show, "Treasures From the Hermitage," and replaced it with this major exhibition on loan from London's Royal Academy of Arts.

It was a fortunate choice, an unprecedented show centering on the work of Cezanne, Gaugin, Van Gogh and Seurate and examining how the influence of these French painters was felt elsewhere in Europe and in the United States. A cheery, colorful extravaganza, it is much in keeping with the spirit of the summer season. That's why British painter Philip Wilson Steer's bright and shimmering painting of children on a beach, "Boulogne Sands" (pictured on page 31), seems a perfect introduction to the exhibition.

The show of nearly 300 works -- some European paintings from the London show have been omitted to make room for examples of American Post-Impressionism, which the National Gallery has added to their exhibition -- chronicles a crucial change in the direction of modern art. That change took place in the later 1880s and was pioneered by the four artists mentioned above Cezanne, Gaugin, Van Gogh and Seurat. These painters were the heirs of the great Impressionist painters -- Monet, Renoir, Degas, Manet, Pissaro -- and the forerunners of the more distorted expressionists paintings of the Fauves like Matisse and Derain and Cubists Like Picasso and Braque. The term "Post-Impressionism" was coined by British art critic Roger Fry to designate the work in a 1910 London exhibition. He simply could think of no more descriptive word since, as the catalogue to the 1910 show observed, the artists included were "able all individualists."

Although Post-Impressionism lacks the coherence of a unified artisitic movement, the paintings in the National Gallery exhibition do say something about the painting of the late 19th century when the Impressionists' dependence on nature and the objective recording of visual experience gave way to a search for emotional, subjective content and an insistence on the individuality of the painter's vision. In general, the art of the period is characterized by attention to color and to the brushstroke itself and by a simplification of design.

These qualities leap out at the viewer of Steer's "Boulogne Sands" -- the bright, flat colors; the short brushstrokes; the simplicity of design reflected in the grouping of the children, in their angular bodies and relaxed, natural poses. In fact, Steer intentionally made the children appear badly drawn in order to create an image of naivete, but he was misunderstood even by his friends, one of whom criticized him for giving one of the little girls "awkward legs." Steer was one of the foremost British Post-Impressionists and nowhere is his understanding of the Impressionists and their successsors in France more apparent than in "Boulogne Sands."

That leads to what is perhaps in fact most revelatory and exciting about this exhibit, more than any single masterpiece -- Cezanne's "Undergrowth," Gaugin's "Contes Bbarbares," Van Seurat's "A Sunday Afternoon on the Ile de la Grande Jatte": Although generation after generation of painters wants to make art that is truly new, few succeed. But the great artists stretch the efforts of their contemporaries and raise the general level of achievement. Few eras have reached such high levels as the brief 20-year period chronicled here.