Clement Greenberg, at 71, should by all rights appear as a large, flat creature, entirely abstract and somewhat resembling a portion of aggressively squiggly wallpaper. After all these years of befriending, defending, promoting and instructing Jackson Pollock and the Abstract Expressionists, it would seem a likely metamorphosis.

As it happens, however, Clement Greenberg has not changed. He has found it more convenient to change the world.

Let us name names here: It was chiefly Greenberg who sold the world on Abstract Expressionism, that explosion of nonrepresentation art (paint dripped from cans, bits of broken glass thrown in, etc.) that put American art on the map just after World War II.

The painting was by Arshile Gorky, Willem de Kooning, Hans Hofmann, Adolph Gottlieb, Robert Motherwell, Jackson Pollock, Franz Kline, Helen Frankenthaler, Clyfford Still, Barnett Newman, et al., but the map was by Greenberg.

If you couldn't follow it, he insisted it was your fault. Greenberg was speaking not just to the befuddled throngs, but to the artists too. In this century he is the classic and problematical example of the critic-as-participant.

Pollock, the best-known of the New York Schoolers (his major paintings now sell for millions of dollars) asked his advice, during working hours; Greenberg did not demur. It was Greenberg who told the color painter Morris Louis to destroy an entire series. It was Greenberg who tried to get the sculptor David Smith to alter his work. Greenberg promoted his favorites boldly, and poured scorn on the doubters. Tom Wolfe, the New Journalist, was so amazed that he wrote "The Painted Word" -- an entire volume of debunkment.

It didn't work. Thursday night, Greenberg could still sell out the lecture hall of the Hirshhorn Museum, at $7 and $9 a head, to continue his cartography. Those who disagree with his lists of good and bad art and artists generate in his speech a recurring word. The word is "stupid."

It is almost too good to be true that Greenberg's first hero was Norman Rockwell. And that one of the first things Greenberg learned about himself was that he had a gift for drawing.

"I was a child prodigy as a draftsman," the critic-as-participant said in the taproom of the Mayflower Hotel, bald of head and greenish of suit, vodka martini in one hand, Camel cigarette in the other, and no apparent arrogance or malice in his aforethought. "Some people have the gift to draw photographically, but just because you're born that way doesn't mean you're an artist."

A teacher at the Art Students League in New York told the young Greenberg that, and Greenberg believed him. "I wanted to paint like Rockwell, or like N. C. Wyeth," Greenberg recalled. "This man -- his name was Leahy -- told me in the gentlest way that my gift was not decisive. So I gave up the notion of a career."

Later, while at Bennington College, Greenberg and Helen Frankenthaler -- both then anonymous -- decided to visit the master at his home in Dorsett, Mass.

"Rockwell met us at the gate," Greenberg said, "and I said, 'I'm so glad to meet you, Mr. Rockwell; you're my idol.'

"And you know what Rockwell said? He said, 'Mr. Greenberg, I would have hoped that you'd outgrown me by now.' We spent the day with him, Helen and I. He was working on a Saturday Evening Post cover. The one where the old woman and her grandson were eating in a greasy spoon restaurant, and looked so out of place. Remember that one?"

Greenberg ordered another pack of Camels and another martini, and then he said: "You have to put Rockwell down, down below the rank of minor artist. He chose not to be serious. But he struck me then as rather happy, and that's the main thing."

Greenberg's life does not seem to have been a search for happiness, but rather for seriousness -- for "major" endeavors in art.

"I much prefer representation painting," he said. "And so do most people. But most people are beside the point, alas. When I came along, abstract art was the major art of the time, and again I say -- alas."

Greenberg saw his first show by Jackson Pollock in 1943, and was drawn to abstract -- a term coined by Robert Coates in The New Yorker -- expressionism almost against his wishes.

At that point, Greenberg paid the bills be serving as an editor at Commentary magazine, and wrote about art in The Nation. It was his critical essays that brought his influence to flower, and eventually to seed (hence the "Greenbergian" progeny now sprouted in every modern museum).

In his collection of essays entitled "Art and Culture," generally acknowledged a masterwork, he reveals his own progress. In 1946 he encountered his first "serious" abstract pictures in the work of Clyfford Still:

"I was reminded uncomfortably of amateur Victorian Decoration. Not until 1953, when for the first time I saw a Still of 1948 alone on a wall, did I begin to get an intimation of his real quality. And after I had seen several more of his pictures in isolation, that intimation became large and definite. And I was impressed, aside from everything else, and as never before, by how upsetting and estranging originality in art could be; how the greater its challenge to taste, the more stubbornly and angrily taste would resist it."

"I've never felt bad about educating myself in public," Greenberg said, "although at first I thought I knew more than I did. I'd taken one art history course at the Univerisity of Syracuse. But in the end, it all falls back to your eye, anyhow."

The problem was -- and for many people, still is -- that Greenberg's eye found "major" statements in abstract canvases, while declaring all the representational painting of the 1950s to be "irredeemably minor."

"In the matter of content, again, you're thrown back on your eye. That's a dilemma for many people, and for many critics, because they haven't read esthetics. If it's good, then it's good content. Mondrian can paint a picture with just four black lines." And someone else, even if he paints Christ descending from the cross, will not have content.

Greenberg, furthermore, does not believe that an artist's personality has much to do with his content. When he deems Pollock "good" and Willem de Kooning "the Pied Pier who has led a whole troop of lemming artists right into the river," it is impersonal, if ruthless.

"You look at the work and not the man," he said. "I was on Partisan Review with Robert Lowell, whom was called 'cal,' for some reason. He was a very wonderful poet, but as a human being, he was a most dreary creature, indeed.

"Of the Abstract Expressionists, Gorky was the only one who wasn't boring as a person, except for Jackson [Pollock] when he was sober.

"Take Pollock, for instance. He was the most radical alcoholic I've ever met. Breath like the exhaust of a truck. One sip of wine would set him off, and yet I valued him more as a person almost more than I value his art.

"When he was himself, and you told him something was no good, he wouldn't grandstand and he wouldn't hold it against you. But when he was drunk he turned into an 8-year-old brat. Your personality just doesn't have a relationship to your art."

It is clear that Greenberg, as critical participant, was quite willing to participate, if not in the making of art, at least in its editing. This is considered rather strange nowadays in an era where the critic usually keeps his distance, pot-shotting from a personal remove. Greenberg, though, was like a theater critic who walked on stage and tried to drag an offending actor off by his ear.

"Morris Louis painted 30 or 40 pictures in 1949 called the Fantasia series, after the Disney movie. I told him to destroy them, but he never got around to it. Years later, I was in India and a dealer got hold of them and sold several -- one is now in the San Francisco Museum.

"Those were awful pictures," Greenberg declared, scandalized that his instruction had carelessly gone unobeyed. "They were supposed to have been destroyed."

In 1972, however, Greenberg was himself the subject of an art world scandal over the works of the sculptor David Smith, who had named Greenberg an executor of his will. It was well known that Greenberg, though a champion of Smith's steel abstract sculptures, abhorred Smith's use of color. He left one out in the rain, and when an art writer discovered what effect the weather was having on the paint, the word "foul!" was heard. Had Greenberg deliberately let nature alter Smith's work?

"Maybe I should have been more guarded," Greenberg replied, sipping a new martini. "But look, Smith had put one coat of color on unprimed steel, and he knew it wouldn't last. He wanted his stuff outdoors, anyhow. Besides, his colors were lousy. Actually, the color never did come off the pieces I wanted it to come off. I think he used submarine paint on those."

Wait a minute, wait a minue, wait a minute.Who's the artist and who's the critic here, anyway? Isn't there supposed to be a difference, Mr. Greenberg?

"Not in David Smith's case."

According to the critic-participant, there is no morality about such things -- only good art and bad art. "Morality is the last refuge of the scoundrel," he said dryly. "I did advise Smith to cut all the heads off his tank totem series, but he refused. And as for the Morris Louises, I did not personally destroy the bad paintings."

What he did, in his clearly written and undeniably persuasive, extraordinary confident and frightfully erudite essays was to inform the world what to think. What stimulated Tom Wolfe was the notion that without Greenberg's yammering and hammering, Abstract Expressionism might not mean anything. As Wolfe put it:

"Modern art has become completely literary; the painting and other works exist only to illustrate the text."

"Wolfe's book is really beneath discussion," Greenberg said, his tone steady. "I suppose I was flattered by the attention, and my daughter -- this was 1973, and she was 11 -- came up and said, 'Daddy, I didn't know you were so famous.' But Wolfe had to be stupid to think I was as stupid as the book seems to make out. So many gaffes."

Greenberg is a hard man in arguments of taste, as his audience at the Smithsonian found. He relies on his; yours is supposed to follow.

"Esthetic criteria -- in music, in dance, in art, in anything -- can't be put into words. I never write my criteria, I wouldn't be that stupid. I've given verdicts of taste, and intentionally not grounded them very well. The reasons why you think the way you do aren't very important. The literary critic F. R. Leavis -- in my book, he's the greatest -- thought he could argue his esthetic judgments, but even Leavis would end up pointing to passages and quoting them. Criticism is just description, adjectives and quotations."

No, Greenberg would not give the audience his criteria. What he would give them was his verdict, regarding pictures in the show upstairs entitled, "The '50s: Aspects of Painting in New York."

"There are two Frank Stellas up there," he said, not blinking. "The one on the right is good. The one on the left isn't any good."