FOUR GIANT LEGS, like those of an elephantine piano, swell up as they go up, eventually making a 2,000-square-foot cantilevered structure. Most of the footage is on one floor, with a library in an aerie.

You enter through one of the 20-foot-high legs, climbing a curving staircase. The stairs are ceremonial - to give you the sense that you are on your way to a very important event - perhaps your coronation - or your beheading. When you finally make it to the top, the excitement is almost explosive.

And so is what you see - great arches, immense circles and a panorama for miles and miles of river and canyon. You have no feeling of being on earth. The cantilever takes you out beyond land to suspend you 155 feet above the river canyon. You don't feel as though you're in an airplane or even in a battlestar, more like standing on the moon looking down at another planet.

Robert Bruno was standing under one of his large steel sculptures about five years ago in his studio in Lubbock, Tex. He thought to himself, "Um, this is a nice feeling. I'd like to move in."

So he began to build a sculpture he could live in.

The monumental size of the structure seems to Bruno to be in scale for Lubbock, in the northwest panhandle of Texas. "The elements are so big and violent here - the dust storms, the wide sunsets. One day the temperature is up to 92, the next 17."

Bruno is 34. He has the muscular, tanned look of a man who spends his day out in the sun shifting, lifting, putting it all together. He has built the sculpture/house himself with little money and no help - a wild and almost impossible fantasy for one man. Not many individual architectural feats are comparable - perhaps Watts Towers. The dedication it takes is immense.

Somewhere at the beginning, you might have expected his wife to say, "You're crazy. You can't do it." But Patricia Bruno didn't. She said, "Go ahead." And just as important as putting up with it, she said she'd help pay for it. They've financed the $50,000 for materials out of their salaries, and private loans. They don't go out much or spend money on other things. They live in a small duplex.

Bruno has been pleased with the way others respond to the project. "I expected my mother to like it - but my stepfather is even more excited about it. Every Saturday and Sunday about 60 or 70 people come out and watch me work. I suppose I'm used to them now."

He doesn't welcome his wife coming and sitting around inside when he's working. "She'll pick up something and drum on a piece of steel, and it really upsets me. It's a dangerous business, and you need all your sensual cues to know what's happening.

"Some architects don't like it much. But the welders love it.I think most people appreciate my devotion to the idea. Even if they don't understand or appreciate my forms and shapes, they seem to like the fact that I feel the sculpture is important. I think that's the problem with too many artists today - they don't think what they're doing is important.

"I like being up there, working on my own. I don't even play the radio, though when I first began to paint as an adolescent, very intense and emotional, I use to play Beethoven.This is different, there is no one moment of ecstasy, it goes on much longer than that. Still, I think my work is closer to Beethoven than to Michelangelo."

Bruno's work has been compared to Antonio Gaudi. "I like what he does very much. But I was this way before I saw any pictures of Gaudi. I spent years being jealous because Alexander Calder already had been where I was going."

Bruno, a graduate in sculpture from Notre Dame, is a professor at Texas Technical University where he teaches sculpture and drawing. Patricia Bruno is the information officer for the regional water company and a maker of documentaries for PBS.

In the beginning, Bruno felt he was about two years away from having his sculpture/house finished. He's felt he was about two years away form having it finished for 4 1/2 years.

His wife is eager to omve in, but he's in no hurry. He "likes the doing of it. It isn't that I want to have the house as much as I want to make it." Since he spends about 15 hours a day every day working on the project, he might be said to live in it. "When it gets too dark to work, I'm too tired to do anything except stretch out and watch the tube."

At first Bruno had to build an hydraulic boom crane, the principal equipment. For the rest he uses an arc welder, small jacks, clamps and other hand tools.

Bruno has jealously refused all help. He wants to do it, as he says, "solo." He made a rough sketch in the beginning, but the house/sculpture grows and bulges and changes with every joint he welds.

"At first I thought the structure would tell me what I had to do. But as I go along, new possibilities open up for me. And I see I am not limited at all. Originally I thought that the outside was the sculpture and I hoped for some space left over on the inside to live in. But as I worked, I saw the inside and the outside are one."

In the beginning he didn't think of the staircase. He still plans an elevator with a glass cup for a cab. Currently, he's thinking about three bedrooms, two with fireplaces, one with its own sitting room; an expansive living room 15 feet high and dining room with a more intimate ceiling. He hopes to go to Louisiana, where a friend lives, to look for black walnut for the floor. The floor will flow over the beams on each side, curling under them so there will not be a hard joint. He might tile the bath. Wherever insulation will be needed, the walls are doubled. He isn't worrying about heating it at the moment. "Cooling will be the problem."

Several of Bruno's earlier sculptures have taken six months or a year to complete, though they were noticeably smaller than this one. He has even made some clay portrait heads. "I like doing the cheeks. A nose is always recognizable as a nose, even if you mess up, but a cheek, you have to work hard to make a cheek."

He's never had a one-man show of his work - except for the house - and he's never sold a sculpture. Last year, Bruno lectured on his sculpture/house and exhibited photographs at the Palace of Fine Arts in Mexico City before the International Architectural Congress.

"I grew up in Mexico City, and I think I learned there that you don't compete with your contemporaries, but with the ages."

And what will he do with his time if he ever finishes the sculpture/house?

"I'm thinking about a five-story building." he said. CAPTION: Picture, "Some architects don't like it much," says sculptor Robert Bruno. "But welders love it." By Tony Webber.