The world according to sculptor Jean (Hans) Arp (1886-1966) was round--deliciously round--or curvy, like an egg, a mushroom cap, a robust female torso. These are the forms that prevailed in his sculpture, woodcuts, collages and tapestry designs throughout his life.

But swirling around him in his early days were the harsh, rectilinear geometries of other early abstractionists--the Cubists, Futurists and Russian Constructivists.

"Arp: The Dada Reliefs," opening today at the National Gallery East Building, asserts that it was Arp who reintroduced sensuous, nature-based biomorphic forms into the visual vocabulary of modern art, influencing the subsequent look of 20th-century manifestations as varied as the Surrealist figures of Yves Tanguy and Al Capp's comic-strip character The Schmoo.

It also reveals that, as a major figure in the creation of the chiefly literary Dada movement in Zurich in 1915, Arp was the first visual artist to experiment with "automatism," the spontaneous, unpremeditated creation of forms that ultimately inspired Jackson Pollock and the Abstract Expressionists.

Arp's long reach as form-giver may, in fact, be at the root of the fact that his own work has been taken as something of a cliche' in recent years. It has been difficult to look back past his legions of imitators to see his own work with fresh eyes. This small show makes that possible.

The 21 early wood reliefs--here shown together for the first time--focus on the evolution of the Strasbourg-born artist's early style, starting with the Dada days of Zurich in 1915 and on through the 1925 Surrealist phase, ending with famous examples from his classic, mature style of 1929.

But it is the subtle shifts in the shapes and configurations of the early reliefs that are most intriguing here, giving concrete evidence of the ideas Arp was grappling with. All are cut from flat pieces of wood with a jigsaw. Sometimes they are painted. The earliest is the angled, rather clumsy geometric abstraction titled "Crucifixion," dated 1915, and clearly made before Arp had found his own visual language, though the artist called it his "first successful picture."

He moves swiftly onward and upward from there, with natural forms taking over in works such as the National Gallery's own "Forest," a painted piece dating from 1916 in which a Matisse-like leaf is the dominant element. Hanging next to it, however, is another, far more abstract version of "Forest" from the same year, in which specific references are left behind. National Gallery curator E.A. Carmean, who organized this exhibition, points out that the random splattering of radiator paint here (and in a few other pieces here) may represent the earliest use of this mode of applying color in modern art.

The show begins with two "automatic" drawings of the sort that probably served as models for the cut-out wooden forms that make up the most genuinely Dada reliefs--those in which accident and randomness have dictated the final form. "Flower-Hammer; Forest Forms," lent by the Municipal Museum in The Hague, is the most spectacular example in this genre.

According to the artist's brother, these wooden forms were cut by a carpenter, probably in large numbers, for Arp used the same shapes in various ways, sometimes duplicating his own works. If this is not pure Dada--for anything premeditated or mechanical was anathema to the basic tenets of the movement--it must be said that the sheer elegance, careful design and superb coloration of nearly all of the other works makes them hard to square with the notion of accident. If there is any argument with this superb little show, it is only with the title, which might more properly be "Arp: Reliefs from the Dada Era."

A pairing of duplicated works is included here--two versions of a pure Surrealist piece titled "Shirtfront and Fork"--one dating from 1924, and the other made two years later. Arp and his Dadaist ideas were a clear inspiration for the Surrealists, whom he joined for their initial show in 1925. But he was likewise influenced by them in the subject of "Shirtfront and Fork," a temporary shift to depictive forms juxtaposed in mysterious ways--a basic tenet of Surrealism. As late as 1954, he was still allied to this movement, taking first prize in the Surrealist pavilion at the Venice Biennale.

Wit and whimsy were major factors in Arp's art, and "Eggboard" is a classic example. Also a poet, Arp published a long poem in 1927 outlining rules for a tennislike game played with raw eggs and paddlelike egg boards. He called this construction "the game's coat-of-arms."

The show, which reveals a major artist in the throes of experimentation, is the sixth in a series designed to explore important moments in the development of major 20th-century artists represented in the National Gallery collections. It is accompanied by a wonderful newspaper-format catalogue filled with short, readable feature stories about various aspects of the artist's work.

The show continues through October 30.