The show of 21 Art Deco posters from the Library of Congress, opening yesterday at the Hirshhorn Museum, reminds curator Frank Gettings of a story:

A ship owner asked A. M. Cassandre, the French poster artist, to design a poster for his company. Cassandre shook his head, and said, "Do you really want me? Remember, I did the poster for the Normandie, and you know what happened to it."

Today, the Normandie, which burned Feb. 9, 1942, and was then shamefully cut to pieces for salvage, is chiefly remembered by Cassandre's magnificent poster.

He presented the ship head on, a sight to shiver your timbers indeed: the great black hull steaming through the waters, a faint lip-shaped foam rising from sea, a flock of birds floating barely ahead.

The poster promised the streamlined life -- the chance to sit way up there on that white deck and wave your hands at all those peasants on the dock. Looking at its great smokestack (rising proudly in a rigid line from exactly in the middle of the picture) you could hear the foghorn's derisive sound. The poster suggested a world of all the caviar you could eat, crepes suzettes in gourmand abundance, women with marcelled hair, obsequious stewards and bachelor bon vivants.

The Normandie was the ultimate in Art Moderne. Her gilded, sleek chic was calculated to make first-class passengers feel as though they were transported to a world where everyone was a millionaire and everybody had avant garde taste.

Cassandre's poster was able to promise all of this by using the same design sense that produced the opulence with elegance of the ship itself. He eliminated every unnecessary line from the picture, leaving only the soul of the liner.

The Library of Congress has about 70,000 posters, of which 20,000 are American. The Library still collects posters, many through copyright registration. The oldest is a 1856 woodcut circus poster 11 feet wide. The holdings, curated by Elena Millie, proclaim acrobatics, theater, motion pictures, Nazis, American politics, food, soap and beer.

Faced with such a feast, Gettings, the Hirshhorn's prints and drawings curator, decided to settle on posters of a particular period. "Art Deco," a bastard but catchy term coined by Women's Wear Daily, is properly called "Art Moderne." The time is the Era of the Last Dance -- the two decades or so between the wars, from about 1918 to 1939.

The most striking of the posters are the ones advertising transportation, usually in stark black and white, sometimes sparked with color. Cassandre's "Etoile du Nord" uses lightening white lines against a black field converging on the start of the destination. Ottomar Anton's "Hamburg Amerika Linie," 1930, rides on a stylized border of waves. A. J. Van't Hoff's "Holland America Line," also 1930, is a marvelous confluence of images streaking through the waters.

Getting points out that the poster artists were all influenced by the avant garde art of the period: the cubists and the futurists especially. They went back to the Mayans and the Egyptians for other ideas -- one wag has called Art Moderne "Aztec Airways." The typography, as with Art Nouveau graphics, is as important as the illustration. Both are integral to the design.

Not all are as slick and sophisticated as the transportation posters. At the head of the escalator, Gettings has placed the cheerful and almost bawdy "Mistinguett" Moulin Rouge poster by Charles Gesmar.

With posters now bringing prices as high as $52,000 in the auction houses of the world, museums are beginning to wake up to their importance. They may be "only" popular art, but they reach people in a way that easel art can't -- or won't.

The show closes Oct. 5.