AFTER A seemingly sonambulant decade, "earthworks" - manifested as land projects, environmental works, site sculpture and miniature archeologies - have suddenly emerged as the most vital new art of the 1970s. It is a form that has already produced some of the most indelible and spetacular sculptural monuments of our time - notably Robert Smithson's "Spiral Jetty" in the Great Salt Lake. More important, it has given artists a re ic and a range of subject matter and media only now beginning to be explored.

The catchwords of art do not yet successfully encompass all that has grown out of the "earthworks" phenomenon and its minimalist and postminimalist ideologies. In its art context, the word "earthworks" itself - originally a military term, as is avantgarde - currently refers to the huge works made of bulldozed earth and stone that American artists began to make in the late 1960s.

But its meaning has expanded with use, and is now taken generically to include large-scale works made of fabricated materials like steel and concrete, as well as natural material like earth, rock, grass and trees. "Earthworks" can also describe any work bound inextricably to its outdoor site.

It was in the mid-1960s that Carl Andre and Robert Morris first talked about site-specific sculpture and "post-studio," as suggested by Andre's suggestion that "we may actually be seeing the end, not of gallery or museum art, but of studio art." Smithson, Michael Heizer, Walter De Maria and others headed for the deserts of the American West to expand on those ideas and fulfill the prophecy.

Fed up with the commercialism of the art world, disenchanted with the commercialism of the art world and with urban culture, and newly aware of the environment, they were dissatisfied with the state of the increasingly cold and vacuous minimalist art of which they had been early and creative practitioners. But their objections were even more profound, according to Heizer: "The desire to engage the larger concerns of the landscape, its character and our relation to it, was an expression of dissatisfaction with the limited concerns of painting and sculpture perse."

Sculpture and painting had for centuries dealt with the landscape, and on many occasions down a splendid job. But the traditional landscape artist painted pictures of what he saw: imitations of the land, the light and the space. The post-Duchamp, Minimalist esthetic had dismissed this kind of illusion as a relic from centuries past.

The makers of "earthworks," in trading brushes for bulldozers, also traded the illusion of landscape for real earth, real light and real space. In the bargain they also got the movement of the sun and the celestial bodies, the passage of time and the miracle of growing things as potential subject matter and expressive media. The artist had returned to the lanscape with a new palette, and it was a palette armed not with pigments but with the infinite material of the outdoors. The revolution was as profound as any in recent art.

Since then, increasing numbers of artists have taken and expanded these new possibilities, with evidence most apparent in last summer's Documenta 6 exhibition in Kassel, Germany, the largest collection of these works ever assembled. Artists from as far away as Japan, Israel and America were invited to go there, pick an outdoor site in a huge park, and create a work related to that site. There the variety and profundity of the newest work in this genre became clear. It was also clear that the term "site scuplture" better described the broadened scope of these second generation "earthworks."

There was, for example, a rich and complex piece by Canadian-born New Yorker George Trakas called "Union Pass," which consisted of intersecting wood and steel bridges that required, and managed to arouse, all the senses and perceptual apparatus the viewer-participant could muster. There was also a mood-making stone environment by Robert Morris, something of a cross between a Zen garden and Stonehenge - as are so many earthworks - and a more sculptural piece made of cast concrete modules by Israeli Dani Karavan, who chose light and water as his expressive language.

Set off by itself on a vast expanse of grass was Richard Fleischner's lush and beautiful "Floating Square," a "sod drawing," he called it, 32 meters square, which consisted simply of a slightly raised square-shaped mound of earth contiguous with the surrounding lawn. Irresistibly lured to this quiet "event" in the landscape, visitors lolled, basked in the magic of the piece.

The involvement of spectators in these works is a crucial element, for they are perceptual and experiential. Private and intellectual in the beginning, the "earthworks" of today, and the site-sculptures that grew out of them, express an increasingly democratic and nonelitist viewpoint, and a desire to involve everyone, not just "art" audiences. "I'm mostly interested in working with spaces that people respond to," says Richard Fleischner. "What they're called doesn't matter to me."

American visitors to Documenta were, in fact, apalled at the way children were irreverantly climbing and jumping (and occasionally writing) all over the works, particularly Dani Karavan's tall, elegant piece. But Karavan was ecstatic. "They love it!" he exclaimed as a youngster reached the top in exultation. Taking up the cue, the grownups threw off their stuffed shirts and abandoned themselves to the work. For this participant, at least, it proved to be the most exhilarating sculptural experience of a lifetime.

The problem with most of the work in this genre, however, is the fact of its geographic inaccessability. In photographs, much of it looks simplistic, and in fact some of its is. Is it enough, for example, to set up huge concrete tubes or structure through which to view the sunrise, the solstices or the movement of a star? Couldn't a pulloff on the Beltway serve the same purpose? Unfortunately, there is no way to make a definitive judgement without giving the work a chance to say what it has to say, which often means an airplane ticket and a jeep ride to a lonely site.

Geography explains why so little critical sorting-out has been directed at earthworks to date. Most critics have seen some of the work, but few have seen all, and the race is on. The public has seen even less. Enough work has been done, however, to extract valid criteria and put them to use. And the matter of criteria has taken on some urgency now that the U.S government, in various guises, seems to have become the chief single source of funding of these works and the artists who make them.

Last month, from the current art Olympus of the Vice President's house, General Services Administrator Jay Solomon announced that his agency is about to commission its first "earthwork" as part of its one-half of 1 per cent for "Art-in-Architecture" program. The artist has not yet been chosen, though all eyes are watching as earth artists, dealers by their sides, descend on Washington to assure that their dossiers are on file. The site will be Norfolk, Va. Meanwhile, Washington light and laser artist Rockne Krebs has already been commissioned to create and environmental piece for GSA in Topeka, Kan.

Just in time to brief the GSA on what's been happening in the field over the past decade is the Hirshhorn Museum's new show called "Probing the Earth: Contemporary Land Projects," a documentary look at 12 completed projects and several others in the proposal stage by 10 artists including Smithson, Heizer, Robert Morris, Richard Fleischner, Nancy Holt, Charles Simonds, James Pierce, Charles Ross and Harvey Fite - all Americans except for the romantic English placer of stones, Richard Long, who showed two gorgeous pieces at the Corcoran not too long ago.

The Hirshhorn show is modest - too modest, particularly in that it fails to give people the one thing without which they cannot possibly understand the impact of these works; that being at least one full-scale land project. Since the Hirshhorn has one of the world's biggest front lawns - the Mall - the omission is particularly unfortunate. Nor does the Hirshhorn show deal with the issue raised by an artist like Christo, the fence-maker and wrapper of buildings, whose art is surely as closely related to the earth as art can be. This and other questions will have to be dealt with eventually in a larger and more comprehensive study in which questions of quality are also raised.

Meanwhile the catalog becomes the basic book on the subject, and additionally provides the amusing service of telling potential visitors where several earthworks can be found and how to get there.

Though earthworks are not objects to be bought, sold and carried home from an art gallery, they do cost money, and the people who make them have to eat. A major source of survival funds for many of these artists seems to have come from the National Endowment for the Arts, either through individual grants, or through matching grants made to cities through the "Art in Public Places" Program.

The first "earthwork" grant, made in 1974 to Robert Morris, was for a piece the city of Grand Rapids wanted for its landmark "Sculpture off the Pedestal" show. It consists of two crossing ramps paved in asphalt, forming an X on a hillside in Belknap Park, an evolving urban recreation area accessible to a large number of people.

Since then, applications for large-scale environmental land projects have proliferated, according to Ira Licht, head of NEA's "Art in Public Places" program. The city of Atlanta received funds to help with an Isamu Noguchi-designed playground there, and a public park in Hartford, Conn., now has an extended environmental stone piece by Carl Andre, which the kids love, though some grownups have taken exception.

A unique offshoot of earth art, currently practised only by himself, Alan Sonfist, is now being funded by NEA to recreate a forest in Greenwich Village, just north of SoHo, which, on the basis of extensive research, will duplicate a precolonial forest that once grew on that spot.

The largest scale environmental project to date funded by the Arts Endowment is one proposed by the San Fancisco Art Institute, wherein six artists, including Robert Irwin and Larry Bell, and one sociologist plan to redevelop San Francisco's entire northern waterfront.

Clearly there is growing social impulse on the part of many of these earth artist. Charles Simonds, best known for his miniature clay architectural remains, has also been much concerned with the revitalization of New York's Lower East Side, where he proposed and built a combined park and playground on a vacant lot owned by the city. He also has proposed the "Stanley Tankel Memorial Hanging Gardens" at Breezy Point, which would cover with wisteria two skeletal high-rise structures abandoned during construction due to pressure from citizens led by Stanley Tankel. Other artists dealing with disrupted space have worked in mines and quarries.

Relatively few land projects have been commissioned privately, Richard Fleischner, (oh for a Fleischner on the Mall) seems to have done particularly well in this respect, with a "Sod Maze" executed on the grounds of a mansion in Newport and a "Turf Maze" for the grounds of former Vice President Rockefeller's home in Pocantico Hills, N.Y.

Several other projects have been financed largely by the artists, sometimes with the backing of their dealers. One of the most fascinating, whatever the financing, is Walter De Maria's "Lightning Field," which when completed will consist of 600 steel poles, spread over a square mile of New Mexico desert. Anyone who has ever seen a desert lightning storm must yearn to see this piece in action.

The question of whether earth works fit the category of art, with all the troublesome qualitative issues such categorization implies, is inevitable. The answer is - and anyone who has seen "Sprial Jetty" will attest to it - that great art has already been achieved in this genre.

But audiences have been deliberately intimidated by much recent art, and their defensiveness is understandable. A recent issue of the American Scholar made a sensible suggestion, however that might break down the defenses and end the hostility that goes with it: Why not simply stop using the word "art" for a while, and call things what they are? Is Stonehenge art?Does it really matter?

With that potential hostility erased, perhaps next time the Hirshhorn could give us not just one but a whole exhibition of first-rate land projects outside on the front lawn, or at least nearby. Otherwise, it seems quite possible that Washington will be on of the few cities in the country where no real earthwork has ever been seen.