ALEXANDRIA furniture sculptor Peter Danko's innovative one-piece plywood chair has been bought by the Museum of Modern Art in New York City.

MOMA will soon display the chair and a model of its breakthrough construction in its design gallery. The Danko chair will be shown with earlier important designs such as the Thonet bentwood chair of the 19th century and the Charles/Ray Eames/Ero Saarinen plywood chairs of the 20th.

Danko's design is a major accomplishment in the centuries-long search for a light, cheap, easily mass-made chair.

Today, the seat of Danko's creations is the back-room shop at his Pond Gallery in Alexandria, where he's made 30 or 40 of the chairs. But a major furniture manufacturer is negotiating for the rights to mass produce the plywood chair, and Danko's designs may soon be as ubiquitous in cafes and restaurants as Eames' is in airports.

The Danko chair comes in two models, with and without arms. Both models are stackable, and the legs of each chair extend farther back than the backrest, so you can shove them up against a wall without marring the wallpaper or paint. Made in one piece, they stay in one piece: There are no screws, no joints to come apart.

Danko had dabbled in one-piece plywood constructions years before he got the idea to send pictures of his work to MOMA.

"It seemed a sane and intelligent way of doing an inexpensive chair," said Stewart Johnson, MOMA's curator of design and architecture. "We suggested he get in touch with some manufacturers about it."

Today Danko is negotiating for commercial production with the same manufacturers who not a year ago told him because so many had tried and failed to make a one-piece wooden chair, he, ipso facto , must have failed too, whether he knew it or not.

"They said, "What you're doing's not new. People have been trying to do it for a long time," Danko recalls. "The chair was right in front of them, but they didn't believe it."

At present the armchair costs $160, side chairs $130. Both are sure to be less expensive in mass production. A design for a lounge chair is also on the drawing board.

With alert but insular eyes sharpened an intensified by glasses, below which his face is inscrutable under a thick but neat beard, Danko speaks in low tones poised with murderous circumspection.

He is concerned that his work be both functional and artistic, or rather sculptural. "Bizarre" is his generic description for a lot of his early work including the "boo-boos" and the "one where I didn't know what I was getting into." This was a two-drawer desk, and rising off women's legs in stacked-wood strata of darks and lights like a desert butte, fraught with hondos 6 feet high and weighing 600 pounds.

There also are seed-pod lamps, handlebar-gearshift/bow-tie lamps and a trestled table that opens like a drawbridge. Danko began "this bizarre stuff" in late 1971, after graduating with a BA from the University of Maryland.

"I spent a long time on sculptures, but couldn't make money on it," he says.

Utility furniture, like the one-piece chair, makes enough money to support him. Danko says he's always liked functional designs almost as much as sculpture. There was the day he saw he had too much "arty stuff" in his room. He thought to himself, "need a table" - an honest table made to do only what a table's supposed to - and built one.

Tables with thickly forested legs, like railroad trestles, ensued. Though be later resigned himself to more functional works for financial reasons, Danko still throws a little sculpture into it. "Optimizing the medium," he calls it. Doing what you want to do while doing what you have to do, reconciling the two as nearly as possible.

But dissatisfaction lingers, as it will in someone who can't quite extinguish a devil-may-care urge to experiment. In the same sentence, Danko defends and despairs of the half-happy medium: Taking about a fellow artist in wood, Danko fatalistically says, "He has good tools, but he's too timid to do something with them." Then he adds, "He's efficient. Wish I was."

But efficiency is a snare, too. Danko thinks most designers don't get such good results "because they don't fool around in the shop." Danko sketches constantly, in mind's eye if no drawing pad is around. As many as a thousand drawings go into each finished design.

A project in the offing is a pair of walnut crutches for an invalid man. These, too, will be "bizarre." Danko predicts, grinning.

The Pond Gallery has been in existence about 18 months. Danko's father designed and built nearly all the machinery in the shop, with materials scavenged from dumps. A tin can is the cutoff switch on his press. The speed control is a bicycle chain, which Danko tugs like the whistle on a steam train as the press comes down to punch out another plywood chair. Noisome glue splotches the floor milky tan and the air with an odor like Brussels sprouts. The glue is exuded onto rollers from an elevated five-gallon drum labeled "Egg Nog Base No. 1."

The Danko chair begins with 10 core sheets of poplar, precut so the grain of each runs at right angles to the other then fed one by one through the glue spreader. They are piled on top of one another as they come out, with extra sheets of wood top and bottom.

It takes seven minutes to stack the sheets, send them one by one through the gluer, stack them again, set them on the press, clamp it down on them and then an hour for the glue to set. "In industry they'd use microwaves and be done in minutes," Danko says.

The press is a mechanism of pure, brute force, weighing as much as a car and exerting 150 tons of force on the armchair, 130 on the sidechair. After molding, there come a couple hours of cutting, sanding and finishing. The time required for this will be reduced by a machine Danko's developing, consisting of "a whole gang of blades going up and down in unison, since the lines of the chair are almost all parallel."

The ability to cut waste is the origin of profit. Danko says, and he uses every scrap of wood. The square piece that's cut out in the process of shaping the front legs becomes the chair's seat. During gluing, Danko puts a sheet of wax paper in the middle of the inch-thick stack of wood, at the point where the legs will be cut. "You don't want a seat an inch thick," he explains, (glancing sidelong to let you know another bizarre revelation is coming), "so you throw it on the floor" - and it splits in two yielding 1/2-inch-thick sheets.