Picasso show reveals how Cubism took shape. Also, pastels display unknown side of Prendergast's work

Few things are as fascinating as the creative process, especially when it involves an artist of genius and the evolution of one of the most important paintings of the age. Unfortunately, since this process generally occurs in private, opportunities for witnessing it on a grand scale seldom arise.

One such opportunity has just come up, however, in the form of a Picasso exhibition that includes preliminary sketches for ``Les Demoiselles d'Avignon,'' his seminal 1907 painting that helped launch the Cubist revolution.

These drawings constitute a major portion of a sketchbook of 80 studies Picasso made that year; they are among the earliest works by him in ``Pablo Picasso: Cubist Works from the Marina Picasso Collection'' on view at the Jan Krugier Gallery here.

Important as they are, however, they barely scratch the surface of this excellent exhibition, which also includes two other sketchbooks, 12 paintings, a large number of individual drawings and collages, and several early prints. All were executed between 1907 and 1926, and represent Marina Picasso's inheritance from her grandfather's estate.

Any show that includes so many early Picasso paintings and drawings would be worthy of special note, but the fact that everything in this one is connected in one way or another with Cubism makes it all the more rare. It is, in fact, the largest gallery show of Picasso's Cubist works ever assembled, as well as one of the most outstanding. From its earliest examples to its most recent, one sees Picasso only at his most authentic and innovative - and occasionally even at his best.

``Head of a Woman'' of 1909-10, for instance, is a major and pivotal work that any museum would be only too happy to own. And much the same is true of ``Woman with a Guitar'' of 1910, a picture that combines delicacy and elegance with serious structural analysis in a manner only Picasso could pull off. And then there's the more solid ``Glasses and Bottle'' of 1914, as well as the sparklingly informal ``Geometrical Composition'' of 1918, and, last but not least, the most densely composed oil in the exhibition, ``Composition with Door and Key'' of 1919.

It's in the drawings, however, that we see Picasso's creative processes most clearly at work and his Cubist formal vocabulary gradually beginning to take shape. We see him breaking up three-dimensional form and then flattening it out and reconstructing it in accordance with Cubist theory, first tentatively (``Study of a Face,'' 1909, ``Mademoiselle L'eonie,'' 1910), and then with increasing conviction and flair (``Man Holding a Guitar,'' 1912-13, and ``Violin,'' 1913).

But most specifically, we watch in fascination as in one small, rapid sketchbook study after another he probes the forms, poses, and structural relationships of several of the figures that will ultimately play a dominant roll in ``Les Demoiselles d'Avignon.''

At the Jan Krugier Gallery, 41 East 57th Street, through Dec. 19. Maurice Prendergast

The discovery of a considerable, so far unknown body of work by a famous painter is always an event of at least some significance, especially if the discovery alters society's perception of the artist in any way.

In the case of Maurice Prendergast (1859-1924), however, whose pastels were brought to light this past spring by Mrs. Charles Prendergast, the artist's sister-in-law, no great changes are expected to occur.

We do, of course, realize now that he didn't merely ``dabble'' in pastel, that he was, in fact, quite serious about the medium for a while. And we now have the advantage of being able to enjoy more of his delightfully colorful works than we could before. But beyond that, our perceptions of his talents and accomplishments will remain pretty much as they've been these past several decades since his death.

Even so, these pastels add a new dimension to our understanding of his working methods. All date from 1910 to 1918, and so represent a later phase of his career. And all, without exception, appear at first glance to have been executed in watercolor.

Closer examination, however, reveals the unmistakable signs of pastel, which is generally worked up to act in counterpoint to, or in harmony with, the watercolor washes, or to add weight, texture, and body to such things as grass, foliage, rocks, and bodies of water.

The overall effect is colorful, lighthearted, utterly charming, and technically about halfway between his early, transparent watercolors and his later, somewhat heavier and more calculated oils.

At the Coe Kerr Gallery, 49 East 82nd Street, through Dec. 5.

Theodore F. Wolff is the Monitor's art critic.