If an art critic from Mars dropped into this year's Biennial Exhibition at the Whitney Museum here, he'd learn very little about the full range of contemporary American art. He would, however, see an interesting sampling of some of its more innovative and extreme tendencies, as well as a few hints about what a few major American artists have been up to these past two years.
He would probably be intrigued by the large scale of many of the works, by the mixed-media installations, and by the fact that film and video play such a large part in this Biennial.
But most of all, he'd enjoy himself - especially if he went with few preconceptions about what constituted art, and with the understanding that some of the things he saw would almost certainly take him by surprise.
During his visit, he'd have his imagination stretched and begin to suspect that intelligence occasionally has little to do with the creation of contemporary art. And when he'd seen it all, he'd probably leave our planet with the conviction that humans are still somewhat simplistic.
That, at any rate, is what my impression would have been had I come upon this show without warning, and without a good three or four years of preparation for some of the ideas represented in it. Without such preparation, some 20 percent of the things included would have been meaningless to me at first glance, and another 20 percent would have seemed downright silly. (It's important we keep in mind that only 10 years ago, roughly half of the things on view in this Biennial would have been dismissed as tasteless and vulgar kitsch.) As it was, I was not surprised by anything, and neither did anything strike me as overwhelmingly silly or bad.
At the same time, hardly anything really impressed me, only a few pieces charmed me, and nothing at all moved me. I was interested, even fascinated at times - but left without feeling particularly enriched or challenged.
That's too bad, especially in an exhibition that is described in the catalog preface signed by all four of its curators as ''a selection of some of the most vital work made within the previous two years by living American artists.'' I challenge that, although not so much on the basis of what's included as what's not.
We can argue all we like (and I would heartily agree) about the importance of artistic innovation and for the pushing back of creative frontiers. But we mustn't forget that art, in its deepest and most significant sense, is about mankind and all his realities - not merely about those that are the most diverting, sensational, or easy to translate into form and color. Art, after all , should do more than follow its line of least resistance.
Based on what he sees in this Biennial, our visitor from Mars might well assume that American art is detaching itself from all larger human and formal frames of reference in order to become a thing unto itself. That it seeks innovatation and experiments for the sake of innovation and experimentation, and will try something new merely for the sake of novelty.
Truth is, American art isn't like that at all. It is rich, broadly based, responsible - and innovative in ways that go much deeper than what is effected through the sort of gimmickry given occasional emphasis in this show. And yet that narrow perception of what constitutes the genuinely new and forward moving in American art lies at the heart of this Whitney Biennial - and lay at the heart of the previous three or four.
One certainly cannot, however, criticize this show for not being colorful and lively. With a few exceptions - most notably Leon Golub's deadeningly vicious ''Interrogations'' paintings, and Eric Fischl's heavy-handed ''Inside Out'' - it simply crackles with life. And if some of the wit and humor seem sophomoric and some of the ideas half-baked, that can, I suppose, be chalked up to youthful enthusiasms overriding all other considerations.
At the same time, I fail to see what the fuss over Jonathan Borofsky's work is all about. And the same, I'm afraid, applies to Robert Colescott and Kenneth Shorr. Jean Michel Basquiat's paintings, on the other hand, always engage my attention, even when particular ones don't quite come off. His ''Untitled'' comes very close to succeeding - but then, unfortunately, it falls flat on its face.
William T. Wiley tops my list of artists whose works in this show I liked, followed by Nancy Graves, Oliver Jackson (he's someone to watch), Mary Lucier, Joan Mitchell, Melissa Miller, Susan Rothenberg, and Mark Tansey.
Of the others, I found Jasper Johns's ''In the Studio'' intriguing, but unresolved; Julian Schnabel's ''Homo Painting'' powerful, but flawed; and Frank Stella's two constructions quite fascinating, but mostly because of what they promise for the future.
It is, in all, an interesting show - as much for what is not included as for what is. It will remain on view at the Whitney Museum through May 22. The film and video sections will be circulated nationally by The American Federation of the Arts.