The National Gallery of Art has purchased a complete set of the 11 progressive states of Pablo Picasso's lithograph "The Bull." They are among his rarest and most revealing prints, for they track the journey of discovery that led him, step by step, to the brink of pure abstraction. In a frenzy of invention, all of them were pulled from a single stone between Dec. 5, 1945, and Jan. 17, 1946. Together they make visible the workings of his mind.

The sequence, now on view in the gallery's East Building, is the only complete set in an American collection.

Only one print in the set, the last one, which shows the bull reduced to geometric outline, was produced to be sold. It was published in an edition of 50. The others, printed in editions of 18, were retained by the artist, who gave some to his friends and left the others to his heirs. The gallery bought its set, through its Ailsa Mellon Bruce Fund, from one of Picasso's children via a European dealer.

The purchase price was not disclosed, but it was probably in the neighborhood of $200,000. A nearly complete set -- state No. 5 was missing -- was sold to collector Norton Simon at auction at Sotheby's in April 1977 for $178,000.

Picasso made these prints in Paris in the lithographic studio of Fernand Mourlot, a master printer he had met through his friend, Georges Braque. There is a story that Picasso, fleeing the November cold of his own small studio, had begun to haunt Mourlot's because the cunning printer had somehow managed to acquire a large supply of rationed coal. Be that as it may, there is no doubt that Picasso fell in love immediately with the medium of lithography. For the next four months he rarely left the shop. He worked there every day from early morning until late at night.

He experimented busily with all the tools at hand--the washes, tusches, crayons of his new-found toy. He was particularly fascinated with preserving what he called "the metamorphoses of a picture," the successive images that let him on his way to a final composition. Nowhere is that metamorphosis revealed more distinctly than in "The Bull."

The beast takes on a strange variety of meanings in Picasso's art. It is sometimes fierce and sometimes gentle, both victim and attacker. In those political pictures in which Picasso shows his loathing for fascism and Franco, the brave bull of the bull ring seems to represent the noble soul of Spain. In other pictures it seems a symbol of Europe's humanism, the bull that bore Europa in the ancient myth. Often in his etchings Picasso seems to use the bull, or its mythological cousin, the Minotaur, to represent himself.

His Mintoaur seduces nymphs, or dies a bloody death, or holds a champagne glass aloft, or, victimized and blind, is led like an Oedipus by a little girl through a starry night. These odd and private images combine in the memory to cast a kind of aura on the prints on view.

The first state of the lithograph, done on Dec. 5, in a thin, translucent wash, shows a wide-eyed animal, sensitive and baffled, whose brushwork somehow calls to mind the brushwork of the 18th-century bull drawings of Fragonard.

The second state, dated seven days later, shows a far more frightening beast. Its neck has thickened, its hide has blackened, its head has been enlarged. "Picasso," writes Andrew Robison, the gallery's curator of prints and drawings, "has transformed his initial drawing into an animal of brute mass and power, as heavy, dumb and implacable in motion as a tank."

The bull's size is reduced in the third state of the lithograph, which is dated about one week later, Dec. 18, 1945. The bull's outlines have grown sharper, its jawline has grown rounder, its hide has become hairy.

The fourth state is dated four days later. The change is astonishing. The focus, for the first time, is not on mass, but surface. The bull's face has taken on the look of an African mask. "White lines," writes Robison, "are scratched across his body like those divisions indicating cuts of meat on a poster in a butcher shop.

In state five, done the day before Christmas, the bull's head calls to mind not Africa, but Crete or ancient Greece. Its eye is like the eyes seen on old Greek painted pottery, its horns have become lyre-shaped.

The bull's head, in the sixth state, dated two days later, has been both diminished and distanced from its body. Its shoulder-hump is now one arc. The increasingly geometrical "patterns of light and dark," write Robison, "even leap beyond his body."

The bull's bulk is reasserted in the seventh state of Dec. 28. Its front legs are a column now, a single graceful line connects its withers, hump and horns.

In the eighth state of the lithograph, dated Jan. 2, 1946, the bull has managed to regain his ear, his mouth, his eye. His front legs are described now by a few graceful curving lines.

The ninth state, dated three days later, displays a radical simplification. The bull's horns have become a single U-shaped line. The darkness that has ruled his image from the start has gathered in his testicles. Small black specks, incomplete erasures, remind us of the heavy beast that he used to be.

The 10th state is dated five days later, Jan. 10. The simplification has increased. The bull's four legs are single lines, his ear and mouth have vanished, his tail has no tassel. The end is now in sight.

The final state, the 11th, is dated Jan. 17. There is almost nothing left -- a tiny circle of a head, a few thin incised outlines -- and yet he is still there, a heavy, vast and graceful beast staring at the viewer with eyes we cannot see. Remnants of the blackness that used to be his hide now float on his body and between his legs, giving him a ghost of weight, but a weight that we still feel.

Instead of a catalogue, the gallery has published a portfolio of reproductions of its newly acquired lithographs. The portfolio sells for $15. About a dozen other prints, all of them Picassos from the gallery's collection, all of them of bulls, also are on view. The exhibition closes Oct. 10.