Joan Mondale was the honorary chairperson for the gala benefit opening of the Merce Cunningham Dance Company at New York's City Center Theatre last month. Afterwards, in the posh surroundings of Regine's scene of the post-performance cast party, she said she "was absolutely bowled over" by Cunningham's choreography - even though she'd never seen his work on stage before.

"I'd read a lot about him, though, like in 'The Bride and His Bachelors' - you know, Calvin Tomkins' book'," she added.

It's not a book - culled from New Yorker profiles and surveying major revolutionary figures of 20th-century arts - for diletantes, and Mrs. Mondale's response to Cunningham seemed wholly authentic.

Just the same, the entire scene - the White House minister-of-culture sans portfolio, Regine's, a first-nighter's list studded with names like Auchincloss, Sinclair and Whitney (mingling with such other spectators as Louise Nevelson, Robert Joffrey, Edwin Denby, Leo Castelli and Robert Rauschenberg) - seemed a bizarre setting for the once scorned, ridiculed and misunderstood iconoclast of the dance world.

No one has been a more potent symbol of the rebelliousness and independence of avant-gardism than Cunningham. Yet here he was in the bosom of avant-chic, and meanwhile, all the radical furor he helped spawn in the dance world over the past two decades seems to have spent itself. Cunningham's work hasn't changed, nor has his attitute towards it, as the City Center opening demonstrated. But the world has moved on. Is it just a case of yesterday's avant-garde becoming today's Establishment, or has the radical impulse in the arts simply been smothered by a world hellbent on "normalcy."

The history of American modern dance is largely a record of inspired heretics, from Isadora Duncan, Ruth St. Denis and Ted Shawn down to Doris Humphrey, Charles Weidman, Martha Graham and beyond - people who refused to fit into the molds history offered them and struck out on startling paths of their own. But no apostasy was ever more bold or eccentric than Cunningham's. His career as a dancer began with Graham - he was, for example, the original Revivalist in her "Appalachian Spring." Having early cemented his alliance with the equally cross-grained composer John Cage, however, he soon turned his back on everything Graham stood for. His choreography renounced story-telling, drama, psychology and even definite emotional implication. He and his dancers moved - in variously surprising, mystifying and untraditional ways - for the sheer sake of moving.

From the late '40s onward, Cunningham left a trail of upset applecarts. In 1951, he composed his first choreography by the use of chance devices - he tossed coins to determine the sequences of movement, their directions and durations. At Black Mountain College the following summer - the place was a veritable "hotbed" at the time - be collaborated with Cage, Rauschemberg, poet Charles Olsen and other in "Theatre Piece," canonized afterwards as the first "happening." The use of "musique concrete" and other forms of electronic sound soon followed. In "Dime a Dance," choreographed to 19th-century salon pieces, the order of which was determined by a member of the audience picking cards from a deck, he anticipated the whole pop art phenomenon, in dance and other media. The movements of "Minutiae" (1964) were derived from "an observation over a period of time of people walking in the streets."

At the conclusion of "Variations V" in 1965, which had film and video imagery by Stan Vanderbeek and Nam June Paik, music by Cage, and electronic devices by Billy Kluver and Robert Moog (the "synthesizer" man). Cunningham rode a bicycle across the stage, and line between moving on stage and off - between art and life - was stretched almost to the breaking point.From the crucible of the Cunningham studio there also emerged most of the young dance hellions of the '60s - including Yvonne Rainer, Steve Paxton, Meredith Monk and Twyla Tharp - who carried Cunningham's esthetic subversions further still.

The ferment of the '60s, however, has long since subsided, and looking at Cunningham's work today, it's lear no more departures are to be effected from that quarter. One of his newest works, "inlets," seen for the first time in New York on that opening night at City Center, had almost a tranquilized air of repose about it. It was "beautiful," in an old-fashioned sense. This is not to say Cunningham has betrayed any of his fundamental principles, or gone soft as an artist.

The old traits are still there. "Inlets" has the same quirky inventiveness of gesture and stance, the same fascinating logicality of connection, the same tantalizing elusivenss that have long been Cunningham trademarks. But the uncharacteristic harmony of components in "inlets" - the smooth, slippery movement patterns, the watery gurglings of Cage's music, the lanquid passage of Morris Graves' huge sun-disc across the rear of the stage - bespeaks no belligerence.

Cunningham retains his mastery, but even in as turbulent and unpredicatable a recent work as the magnificent "Sound-dance" (1974) there are no new esthetic alarms. At 59, Cunningham's days as an idol smasher are behind him and there's no reason for them not to be - it's enough for him to till the vast territory he's uncovered for us in the first place. Cunningham seems aware of all this. In a recent interview, he told critic Marcia Siegel:

"People seem to like our dance more these days. At least they aren't bothered by the music, by the discontinuity. It's how they live now. With television, they can create their own rhythms, switch from one thing to another or listen to one thing and watch another. Then they go to the theater and see it too."

He's doing, in other words, what he always has done, but life has become more-Cunningham-like in the interim.

He may have a point. But that still leaves the question of where today's budding Cunninghams are to be found, in any of the arts. If there are any, they're certainly not in plain sight.

"Avant-garde," of course, has been used to denote a variety of phenomena - art that is in advance of its time, in its novelty of language or concept; art that is simply outrageous, in flagrant conflict with prevailing moral or esthetic standards; art that is deloberatley seditious, seeking to overthrow entrenched principles or powers; or art that is in the "vangurard" simply by virtue of its obscurity or unpopularity. It's only in this lattter-most sense that one can speak of a contemporary avant-garde at all.

But the arts move forward, like most fields of human endeavor, only under the spur of malcontents and restless visionaries. I'm not talking about "progress" now - Webern isn't necessarily superior to Beethoven, nor is Pinter automatically an improvement on Shaw - but about a desirable flow of invention and discovery. An art without an avand-garde is a stagnant art, and that's where we seem to find ourselves at the moment, with the exception of a few small ripples of originality and excitement at the periphery of public attention.

One of the last critical essays by the late Harold Rosenberg began: "The abssence of an avant-garde . . . has begun to seem a normal condition of contemporary art." He was writing about the plastic arts, but the words apply with equal force to other realms. After noting that periodic flagging of creative energy in the arts is not unusual historically, he then warned:

"What is peculiar to our time is that each lapse into torpor threatens to become permanent. The forecast of an ice age, or 'wasteland,' is built into present-day culture. Except for intervals of great inner vigor, the weight of institutional inertia seems capable of subjecting all human activities to mechanical laws."

Have the arts, too, succumbed to this inertia? So many people these days seem to feel immobilized by the mammoth combines of politics, commerce and communication which appear to govern the course of our lives. And these behemoths have well learned the techniques of copotation - anything remotely threatening or disruptive is instantly assimilated into the machinery.

Critic Hilton Kramer has pointed out in considering the same dilemma that the century-old tradition of the avant-garde in art began in the artists' "creative alienation" from the prevailing bourgeois (and philistin) culture. The problem today, he deduced, was that our avant-garde "has dissolved in the embrace of its traditional antagonist."

Look around. Where is the Samuel Beckett, the Edgard Varese, the Jean-Luc Godard - or the John Cage or Merce Cunningham, for that matter - to jar us loose from the banality, the frivolousness, the interminable rehashing of old forms and styles that mostly passes for art today? Where are those who will blast the world from its numbing disco beat and TV narcosis, into some new blaze of awareness and conscience?

Kramer's conclusion, arrived at four or five years ago, was:

"As for the future of art, I have no doubt that it is going to be very like the future of life generally -tyrannized by technology and bureaucracy, rationalized by propaganda, trivialized by the mass media, condemned to an abject dependency on the main course of society until its best instincts recoil in disgust."

In 1978, signs of such disgust are nowhere to be seen. We seem doomed to "business as usual" in the arts for some time to come, and except for the few masters like Cunningham still laboring among us, it's pretty dreary business.