Abstraction - we have just barely begun to understand

It would seem that the great tidal wave of modernism has reversed itself and is headed back out to sea, leaving the masterpieces of our era - the works of the Cubists, Constructivists, and Expressionists, of Brancusi, Picasso, Matisse, Mondrian, Miro, Calder, Pollock, and others - glittering on the beach.

But why, and what does it signify? Has modernism failed, and is it turning tail? Or is it merely that its first great phase is over, and that its motivating forces are returning to nature and to art history for renewal, inspiration, and the replenishment of its creative resources? Or could it be that it's just time for a change?

There is some truth in all three theories. Modernism did fail, at least in some areas, but it also succeeded dramatically in others. Its ideals and driving force, in particular, are very much alive, and in as great a need as ever for formal resolution. There is an awareness, at the same time, that the premises and values upon which the more extreme forms of modernism were predicated were insufficiently broad and deep to sustain that movement beyond a certain point. There is thus, at this time, an extraordinary renewal of interest in primary creative sources, in nature and its appearances, in mythic symbols and systems, in sentiment and primal emotion, and in the great art of the past.

It is also true, of course, that it is time for a change, that 20th-century modernism is increasingly ill-equipped to cope with what we can already see of 21st-century attitudes and realities. More and more of our younger artists are presenting us with alternatives, or with whatever their imaginations and intuitions suggest might satisfy future generations.

We are, in short, at the start of a fascinating (and possibly somewhat maddening) period in which such artists as Miro, Pollock, and Stella will rapidly become ''Old Masters,'' and much of what we now consider advanced will seem reactionary - and vice versa.

The cultural pendulum, in other words, has once again swung from one extreme to the other. But those who now sigh with relief at the demise of modernism - and particularly of abstract and nonobjective art - had better brace themselves for a surprise before long.

The fact of the matter is that what we call modernism lies too close to the heart and soul of art ever to die. And what we call abstraction represents an artistic ideal we have just barely begun to understand. If the days of both seem numbered, and their major accomplishments appear less grand than the masterpieces of the past, it could be because they have been momentarily eclipsed, and because a century hasn't been long enough within which to equal or surpass what it took historic art thousands of years to produce.

Abstraction has many problems and challenges. In particular, it needs to achieve a level of authenticity at least equal to what human beings experience during their constant encounters with observed reality. It must also overcome its tendency to seem contrived and as trivial as a doodle - all of which can cause it to appear less ''real'' and important as art than a precise rendering of a tree or a good likeness of Uncle Harry.

I suspect one reason ''realism'' seems so attractive to many younger artists today is that the issues and problems of abstraction appear so obscure or insurmountable. Under such circumstances, it is easier to start over again in another area - as did those younger artists just after the turn of the century, bringing abstract art into being when the problems related to painting the human figure became - or seemed - irrelevant or impossible to resolve.

What we are witnessing, in short, is merely one of art history's periodic reversals of emphasis designed to give certain ideas and methods a chance to ''rest'' while new theories and old solutions are trotted out. It's difficult to know when or how, but one thing I'm certain: Whatever is valid and valuable in abstraction will once again make its appearance. It may take a century or it may take even less than a decade, but it will reappear.

In the meantime, 20th-century abstraction remains alive and well in the hands of such artists as Richard Diebenkorn, Al Held, Ida Kohlmeyer, Robert Natkin, Ron Gorchov, Terence La Noue, and several others. Each has personalized and carried forward at least one aspect of the modern nonrepresentational tradition, and all have demonstrated that they are among the genuine heirs to the ideas and ideals of this century's great formal innovators.

These artists' styles and attitudes are extremely diverse, and range from the geometrically severe (Held) to the profoundly subjective and open-ended (La Noue), from the sensitively regulated (Diebenkorn) to the brilliantly improvisational (Kohlmeyer) - with Natkin and Gorchov sharing only a passion for color.

And yet their strength - and that of abstraction - lies precisely in this diversity, for it proves that the ideas of the great seminal moderns weren't rigid, lifeless theories, but dynamic impulses fertile and broad enough to spawn a wide variety of art forms, all of which could legitimately be described as abstract. And none of which could be viewed as representing the swan song of modernist abstraction.