Piet Mondrain's life spanned two centuries and almost every major movement in mordern art. And he emerged with a style which even today is utterly distinctive.

"I don't know of anybody quite like him until just before Frank Stella in the '60s," says E.A. Carmean Jr., the Curator who organized "Mondrian: The Diamond Compositions." The show, which opens tomorrow at the National Gallery of Art and continues through Sept. 16, contains eight of Mondrian's 16 diamond-shaped paintings known to exist, along with supplemental drawings.

Born in Holland in 1872, Mondrian began as a traditional landscape painter. He was soon drawn to Impressionism, Fauvism and Cubism, but gradually strove to free his art subjects which would have associations for the viewer. Finally, in Paris after World War I, the abstract-geometric style he pioneered reached maturity.

For the next 25 years until his death in New York in 1944, he continued to develop subtle, iconclastic changes in the heavy vertical and horizontal compositions of rectangles and squares for which he is best known.

The diamonds are a famous variation. Although he painted only a limited number of them, they are spread throughout "almost every phase of his mature career," Carmean says.

Though there have been considerably larger Mondrian shows elsewhere, the diamond works have never before been studied in what Carmean calls "isolated unison."

One of the two centerpieces in the Gallery's own imposing "Diamond Painting in Red, Yellow and Blue," painted between 1921 and 1925. It is a bold work that would seem stark were it not that the coloration of the rectangular elements is so carefully calculated (all separated by heavy black bands) that they give an impression of liveliness rather than austerity.

Mondrian's last work, and a principal piece in the show, is "Victory Boogie-Woogie" (1943). It reflects a fascination with the character of American popular arts that began long before he moved here in 1939.

"Mondrian began writing on American jazz as early as 1919," Carmean discovered in Paris last year. "He adored torch singer Josephine Baker, and though he was hardly an affluent man, he would sit in various clubs and watch her dance. He also said he liked mordern dance because the figures never touched each other.

The last American paintings are much busier than most of his mature work, with their far larger number of smaller rectangles alternating with larger ones. But Carmean doubts that America made the difference and suggests that the word "Victory" in the last composition might as easily refer to the "Victory' of his esthetic aims as to "Victory" in World War II.

Still, the war affected is last years. He left Paris for England because he was convinced Paris would be bombed," says Carmean. "Instead, of course, he got bombed out and Paris didn't."

Mondrian was neither a Cubist nor an Impressionist, though he combined elements of both - at least conceptually - and came up with something new.

He certainly owed something to the abstraction of Cubism, Carmean believes, but he carried if further than Picasso or Braque.

Carmean writes in the lucid, exhaustive catalogue for the show that by 1914 "Mondrian had transformed the cubist scaffolding into a grid that spreads out laterally like a screen."

In 1942, Mondrian described his earlies work this way:

Observing sea, sky and stars, I sought to indicate their plastic function through a multicity of crossing verticals and horizontals."

If the Mondrian canvases appear to have the simplest clarity, close examination and electronic analysis show that there was nothing simple about their evolution. "Victory Boogie-Woogie" went through three basic repaintings on the same canvas over two years, typical of the artist's agonizing concern with structure.

Oddly enough the perfectionist painter was less interested in color. "Sometimes," says Carmean, "he would actually leave those decisions to the patron.

"There was one exception, though. For some reason he hated green - even to the point that after his walks through the beautiful English countryside, he would carefully pick all the grass from his trousers and shoes." CAPTION: Illustration, Mondrian's "Diamond Painting in Red, Yellow and Blue"