Think a bit about fruit flies devouring vegetables in the fields and fuel costs making it more expensive to ship produce from afar, and you will understand why Witold Kuncewicz believes he has the future by the tail.

Kuncewicz and his wife Dorothy don't turn a spade of dirt on their little spread near Flint Hill, Va., but they are pioneer farmers in an agricultural field whose time either is nearing or is here already.

They grow vegetables hydroponically. No soil, no fertilizers, no pesticides. With only seeds, water and nutrients in a year-round controlled climate, they have a hydroponic farm.

In two 130-foot-long plastic greenhouses that sprang from their crazily logical brainstorm, the Kuncewiczes have created a hydroponic system that produces nearly perfect, succulent heads of lettuce in commercial quantities for Washington-area food stores.

The Kuncewiczes are not alone. Hydroponic vegetables are being raised on a small commercial scale by several other pioneers in the Washington area. Leafy items, tomatoes and cucumbers seem to be the most adaptable to hydroponics.

At first blush, this might seem to be backwards farming. At second blush, hydroponics may very well be the future for vegetable growing in areas like Washington, distant from the cornucopias of California and Florida.

"Hydroponics is the wave of the future," Kuncewicz said the other day, standing amid deep green heads of lettuce pushing up from their water source on long waist-high tables. "In these greenhouses, we can produce 10 times the volume of vegetables that can be grown per square foot outdoors."

That already is happening around the edges of many European cities, but there is equally good reason for Kuncewicz's optimism here in the eastern United States. Several major agribusiness firms, Archer-Daniels-Midland Co. and General Mills among them, agree and are moving into hydroponics with major projects.

One of the more obvious appeals of hydroponic growing is the mounting cost of transportation. As fuel costs increase, the price of hauling, say, a cucumber from California or a winter tomato from Florida increases. Department of Agriculture experts say it costs 15 cents to send a head of lettuce from West Coast to East Coast, 8 cents more for a can of tomatoes. Sooner or later, an Eastern consumer may pause before paying the price.

California's experience this summer with the Mediterranean fruit fly is another reason for hydroponics. A sudden or uncontrollable infestation in the traditional growing areas means scarcity and high prices in consuming areas.

"It is expensive to get started, but any way you look at it, it is rational to grow many vegetables hydroponically," Kuncewicz said. "The main reason it hasn't made much headway until now is that before the age of plastic the price was prohibitive -- all the glass you needed for a greenhouse."

This all came to Kuncewicz during a visit to his native Poland in 1972. He found belts of greenhouses outside many cities, where fresh produce was being raised, and he found that greenhouse operators were among the most prosperous of Poles.

He and his wife came home inspired. They would build a greenhouse and maybe even prosper. It turned out they didn't know what they were getting into. They couldn't get much information, there weren't many people growing vegetables hydroponically and they had to go about their scheme by trial and error. By 1975 they had learned enough to begin growing vegetables.

"We have $100,000 invested in this much of it through a Farmers Home Administration loan , but it should have cost us $50,000," Kuncewicz said. "We made a lot of mistakes because there are so many little things that can go wrong. But we have worked those things out and it has evolved from an experiment into a commercial operation."

Plastic plays a major role in this. Each greenhouse is covered with two layers of sheet plastic. The growing tables are made of corrugated plastic, over which the water flows. Each table is covered with a plastic sheet, with slits through which the water-nourished root bases grow into plants. Plastic pipes carry the water (only 250 gallons, recycled constantly, are used); plastic tubing carries air that warms the greenhouse.

Individual seeds are planted in tiny water-absorbent cubes and allowed to sprout in the nutrient-laced water. The sprouted cubes then are put on the plastic-covered tables and allowed to grow to harvest size, a process that takes about 30 days.

From this, the Kuncewiczes' refrigerated truck every week takes more than 2,000 head of freshly picked ostenata -- a variety similar to the more common Boston lettuce -- to Giant stores in metropolitan Washington and to several other markets around Warrenton and Marshall, Va.

With this, the Kuncewiczes figure they are close to breaking even. After they erect a planned third greenhouse, with cost-efficient solar heating to maintain a steady 75-degree temperature, they think they will turn a profit. The future includes expansion into endive, a potentially more lucrative crop than lettuce.

"We get many visitors here and we tell it like it is," Kuncewicz said. "It is a seven days a week job, just like dairy farming, and you have to have long-term dedication, a stout heart and, in the beginning at least, a source of income from some other place."

Kuncewicz has solved that by turning over operation of the hydroponic farm to his wife while he works as an executive with an industrial firm not far from Flint Hill.

"Rational" is a word that keeps coming through every explanation Kuncewicz makes for his hydroponic farm. As in: "It is rational -- you provide fresh produce at the same price of tired old produce that you find in most stores today. No need for tired old produce. That is rational."