Back rooms of galleries are great places for discovering art

I love the back rooms of galleries - as well as museum storage areas, curators' offices, and artists' studios. All of them house art treasures the general public often never sees.

It's not that there's an art-world conspiracy to keep certain choice items from the public, only that there's not enough space to show it all.

There are also other considerations. A gallery dealing exclusively in very recent work may have bought a special Degas pastel or Ingres drawing for an exceptionally low price. Since the gallery may not think it appropriate to hang it next to its wild and woolly Neo-Expressionist paintings, it either has to keep it or sell it through other channels.

In the meantime, it hangs over the dealer's desk in his back office, and is proudly shown off to anyone thought capable of really appreciating it.

Or a dealer might have bought something special for a favored client and can be persuaded to show it to a few friends before making delivery. Then again, he might want the reaction of a few fellow art-professionals to the work of an artist he's considering adding to his ''stable'' - or an opinion on a work's authenticity, importance, value, or date.

Whatever the reason - and these are only a few of those possible - I know that when a dealer invites me into his back room or office, I'm probably in for a pleasant surprise.

Such was the case a few days ago during my visit to the Jack Roth exhibition at M. Knoedler & Co. here. I was enjoying the show immensely when I was approached by one of the gallery staff, who asked if I cared to see something else of interest. Since nothing could have drawn a ''no'' from me, I followed him down to the temporarily closed lower gallery, which was filled with huge canvases, some stacked but others leaning face outward against the walls.

These, I was told, were recent paintings by John Walker, an artist not yet sufficiently recognized in the United States but widely acclaimed in Europe and his native England.

''Now, thatm is painting!'' was my first remark - as well as my last, just before leaving the gallery almost an hour later.

And indeed it was. Every one of the canvases I had access to had that wonderful painterly immediacy that differentiates the work of an artist who ism a painter from one who merely uses paint.

This painterly quality is rarer than one may think. Relatively few artists (even great ones) are true painters. An artist's talent or genius may find expression more readily through drawing or line, or through the organization of colors and shapes. Or then again, an artist may be extremely cerebral and find his truest creative identity through the invention of new forms or styles.

Thus Michelangelo, while he was a very great sculptor, draftsman, and formal inventor, was not a true painter in the sense of Rembrandt, Velazquez, El Greco, and Monet. (Great as they are, Michelangelo's paintings, in the strictest sense, are really magnificently tinted drawings.) And Picasso, in our own day, also realized his genius most profoundly (although certainly not exclusively) through line.

A true painter expresses himself to a large extent through the physicalitym of paint, not merely through the colors paint might assume, or the forms it might help define. Such an artist may also be a brilliant colorist, and have all the other attributes of art, but if he is a real painter, a crucial element of his art is transmitted through the ''feel,'' texture, and weight of the paint itself.

Unfortunately, this is not well-enough understood, most particularly in relation to certain modernist painters. The artistic identities of such established artists as Jawlensky, Soutine, Pollock, Johns - as well as of such newer painters as Tino Zago and Terence La Noue - depend to a very large degree on the rich physicality of paint. These artists' willingness to commit much of their art to that physicality is not understood by many, especially by those who want their art more traditionally neat, tidy, and less turbulent.

At any rate, the paintings by John Walker I was being shown in the lower gallery of M. Knoedler & Co. were passionately painterly - and extremely powerful to boot. They convinced me immediately that Walker is a remarkable artist, and that what he is doing is of considerable importance. He obviously has a clear and shrewd insight into the various modernist traditions, and the ability to distill whatever he wants of those traditions and to intergrate them into his art. It's a rare talent, and a valuable one. But for all that, it was the power and immediacy of his paint handling that really convinced me of his worth. He simply is a painter.

The public will be able to judge that for themselves, however, when his work goes on exhibition for three weeks (April 2-21) at M. Knoedler & Co. It should be quite a show.