Welcome to the town with the newest real estate notion in America: the underground condominium. Here the well-to-do modern caveman and his family can hide from their nightmares of nuclear or domestic calamity.

The thing is called Terrene Ark 1, a 240-under three feet of earth and eight inches of reinforced concrete -- and which will be equipped with decontamination chamber, air and water filtration systems, independent utilities, a clinic and trauma center and round-the-clock protection from potential invaders.

Each diminutive apartment will be supplied with a year's worth of dehydrated food stashed behind the walls and under the beds, and will come furnished with nostalgic reminders of the real world -- artificial potted plants; paintings of forests and waterfalls; flowery fabrics on the furniture, and more floral patterns on the shower curtains and tiles and engraved into the bathroom mirrors.

These condos will have everything except a view, and yet even that is being simulated. Interior sliding windows will look through to pastoral murals to afford what is called "psychological medication."

This is the vision of life after the fall, as beheld by the founders of Survive Tomorrow Inc. If it's pretty grim, at least, they say, it beats surrendering to the brutish forces they see closing in on us.

Terrenc Ark 1, being built on 7 1/2 acres at the edge of this quiet town in southwestern Utah, is merely one manifestation of the new growth industry of survivalism. Uncounted hundreds, even thousands, of Americans who expect a breakdown of law and order, particularly following economic disaster, nuclear attack or natural catastrophe, have retreated to rural hideouts to stockpile guns, C-rations, camouflage jackets and radiation suits, and to train themselves to fight for what they've got.

The Ark builders, instead, advocate "group survival." In a prospectus for the project, its creator, Ronald Brent Boutwell, writes:

"Only group survival allows for pooling of resources and a continuing cohesive society unit. You know who your friends are! The 'head for the hills' individualist or small groups are weak prey of the desperate, and each outsider is a potential enemy. Only group survival can provide the necessities of civilization such as security, organized militia," and so on.

Now is the time, says Boutwell, to "pick a place, choose your friends and then get prepared" for the worst.

This is strong language, and yet the man behind the death-defying Ark Hardly fits the image of a fanatic.

Ron Boutwell is a 47-year-old lawyer and engineer, a trim, gray-haired and personable man who has fathered eight children. Born and raised in northern Utah, Boutwell spent the first two decades of his adult life in California. As an aerospace engineer there, he worked on the Atlas and Poseidon missile programs "when we were strong militarily . . . before it went down the tubes." As a city attorney, he witnessed the social disorganization that is Southern California. "It kind of gives you a feeling of what's coming," he says, and in 1971 he brought his family to this sparsely populated valley rimmed by red mesas and volcanic mountains.

He's not alone, he says, in believing that the social order is coming apart. "So many people have that gut feeling." Besides, "The history of the world has been nothing but problems and wars."

When the crunch comes, survivialists predict, it'll be every man for himself -- guerrilla war between the haves and the have-nots -- and it's definitely the haves who are buying units at Terrene Ark 1.

In the offices of Survive Tomorrow (which are across the road from the town cemetery), Boutwell shuffles through a foot-high stack of inquiries about the Ark: from a bank examiner in Houston who fears economic collapse; from a U.S. Army intelligence man in Virginia who fears atomic holocaust; "from professors and stockbrokers and doctors," he says, "from people who've armed nuclear bombs." Their average age, is estimates, he 50.

Since the condos went up for sale in mid-January, at prices ranging from $40,000 to $80,000, more than 60 people have made cash commitments, says Boutwell. Because Survive Tomorrow, the developer, is still working out mortgage arrangements, some of the initial customers have paid cash for their shelters. "They're just buying blind!" declares the amazed Boutwell.

Between now and Armageddon, the condos are meant to be used as vacation homes or guest houses. Boutwell, like some of his customers, is having a house built above ground near La Verkin, as well as securing a unit in the Ark.

In the meantime, he has founded the American Survival Association, to bring together the disparate Cassandra movement. The ASA's first newsletter, published in March, rails against the federal government's half-hearted civil defense program; against the nuclear policy fo mutual assured destruction; against the Soviet menance in general; against the "self-perpetuating monster" of public welfare. The ASA is also organizing a "survival school" to train people in self-sufficiency and self defense.

Boutwell objects to the idea that the Ark is a venture in dog-eat-dog selfishness, He disassociates himself from survivalists who "wave guns and talk about shooting people" and insists that "our philosophy is to preserve society and its laws." He says, "We're here to cooperate with the town of La Verkin," and points out that the medical center, when built, will be available to townspeople -- except in times of emergency.

As for the rest of us, Boutwell is merely sorry.

He's afraid that city-dwellers will be goners if society crumbles. "In a city," he asks rhetorically, "what chance has a man got to keep his stuff?" Gangs will run amok, he says, "like after the Civil War." And yet, if the city people try to escape, "they won't have enough gas to get where they want to go!"

Boutwell, brimming with self-satisfaction, has to laugh at that thought.

Tom Lindsay, an affable former military pilot who is the accountant for Survive Tomorrow, points out La Verkin's enviable location on a large map of the United States overlaid with glassine projections.

The first overlay purports to show "panic distribution patterns" during a disaster. He observes that people fleeing the Salt Lake City metropolis would have to drive 330 miles to get to La Verkin.their tanks would probably run dry, he says, a little ruefully. "They'd neve make it."

There is some concern, he admits, that hordes will arrive from Las Vegas, only 130 miles distant.

It's a delicate dilemma, he explains. "We don't want to have to turn people away" from the Ark, and yet in the final analysis "we want to make sure we ourselves survive."

The overlay map for population density shows La Verkin to be happily lonesome. The annual-snowfall overlay shows La Verkin to be in a temperate zone. The active-seismic-zones overlay shows the ground to be stable. The overlay marking primary nuclear targets and fallout patterns gives Lindsay further comfort, although he concedes that the MX missile system, if built, would bring the danger closer. "We're not real pleased with the MX," he says.

Survive Tommorrow is not putting all of its fragile eggs in this one basket, however. Other Terrene Arks are planned, and Lindsay points out two possible locations, in northern Michigan and Florida.In choosing a site in the populated East, he says, "the biggest problem is security. We can handle the fallout a lot better than we can handle the people."

Civil strife could break out at any time, he cautions. "As Reagan cuts back on welfare aid and food stamps, people are going to get angry."

On the table next to him is a copy of Howard J. Ruffhs best-selling book, "How to Prosper During the Coming Bad Times." On the wall is a poster urging corporations to "insure survival of your business by protecting your key business personnel and their families" and to "consider relocating certain key business offices and/or key production facilities to our area in safe underground survival facilities."

Lindsay shows me through the two model condominiums in the basement of the Survive Tomorrow headquaters. The apartments are so small, the tour takes but a few minutes.

The one-bedroom unit, intended to house a family of four, measures 12 by 30 feet. The three-bedroom model, designed to shelter as many as 12 people, measures 24 by 30. In such crowded conditions, one wonders, wouldn't law and order break down within the family itself?

Lindsay shows where the freeze-dried food is hidden: in wall cupboards; in the ceiling apace above the bathroom; under the beds; under the dinning booths. He notes that each unit comes equipped with a color TV and that the Ark will have its own satellite receiving station. There will be saunas, he says, and racquetball courts and an animal shelter, all connected through subterranean walkways. There will be a library, a workwhop, a religious center.

He is particularly intrigued by the idea of interior windows. It's an austere environment to be in 100 percent of the time without this window," he says -- not a window exactly, but "a trick in your mind to make you think you're looking through a window."

The developers' latest idea is to install ceiling windows through which occupants could view photographs of the sky and, at night, the starry heavens.

All in all, Lindsay maintains, Terrene Ark 1 is proof that people "can survive in comfort."

He himself, like Boutwell, has a family of 10. He'll need a three-bedroom sanctuary.

Salesman Hector Spencer strolls into the model apartments with four prospective buyers in tow. They are two elderly couples from South Dakota, and they're mildly impressed as Spencer reveals the food caches.

One man says, "I'm worried about the last loaf of bread and who's going to get it."

His friend replies, "The first one to get to it."

One of the women remarks, amused: "Then all the little rats are going to run to their cubbyholes." She says, "That would drive me crazy, to live underground. It would give me claustrophobia. I like the wide open spaces."

As the salesman explains about security measures to be taken in case of a crisis, the first man reasons, "If somebody comes to the door, you can't just turn him away."

"If it comes to that," the woman says, laughing, "I'd take my chances up above."

The other woman agrees: "I think I'd rather face the music.