In an August swelter that exhausts all color, the tomatoes are a vermilion shock. Sickles of purple eggplant, golden melons, swamp-water cabbages and gilt-haired corn spill out over a palette of wood bushel baskets.

"Here, Picasso," says Pennsylvania fruit farmer Aubrey King, waving a small fruit knife toward a browser in an art print T-shirt. "Have a slice of peach."

This is the Wednesday farmers' market in Fairfax, a weekly watercolor of home-grown produce sold from the back of a dozen pickups in the parking lot of the government center on Chain Bridge Road.

In this curious concrete casbah, a vivid clutter of cafe umbrellas and makeshift canopies, these sturdy tailgate vendors dangle the lures of taste and smell before a crowd of county workers and casual connoisseurs.

"It won't bite you," King says to a small child who may never have seen a peach in the wild. And bending, he offers a dripping slice straight off the blade. Two yards away, another vendor is stabbing long triangular wedges from the heart of a watermelon, and an open cantaloupe shows the moon craters of previous samplings.

The air is sweet with the scent of basil plants and sharp with the sweet-sour tang of tarragon. The pyramids of summer melons, cream-colored and crowded together, reflect the polyester shoulders of young women rounded above them.

"Where are these from?" they will ask, as self-consciously knowledgeable as a new-car customer preparing to kick the tires. And King answers, brushing one hand across the front of his stenciled purple T-shirt, that he comes from the Twin Springs Fruit Farm in Orrtanna, Pa., 15 miles west of Gettysburg and a 2 1/2-hour drive from Fairfax.

"We really appreciate people coming to places like this," says King, a 35, a Baltimore native who, with his wife and three other couples, operates the 95-acre farm as a partnership, selling from a roadside stand and weekly markets in Arlington and Takoma Park as well.

"People don't drive up into the country on Saturday and Sunday the way they used to. The guy who had the stand for a decade before us used to do good business, but these days you have to come to the people, to the metropolitan area.

"We've had this farm for five years--peaches, plums, nectarines, apples, pears, some berries," says King, tall and shaggy, with wire-rimmed glasses. "We don't have great financial planning or anything, we're just trying to survive." He weighs a bag of peaches on an old-fashioned enameled grocer's scale. "It's one thing to inherit a farm with a 30-year mortgage and a nice low interest rate, but to buy one now."

Next to King is Harry Brown, owner with his wife Marjory of the Moenkopi Farm in Lovettsville, Va. Backhanding watermelon juice off his chin, Brown translates Moenkopi as "place of running water," named for a Hopi town near Flagstaff, Ariz.

"It's about 50 miles from here," says Brown, a former U.S. Department of Agriculture employe who took to farming when he retired three years ago. "I have 22 acres, but I only farm two or three." Reaching over his stand to accept cantaloupes a customer has selected, he juggles first one, then the other in a pair of free-hanging metal justice scales. "It's just a little extra money . . . two or three hundred dollars' worth of produce every week."

Although most of the customers say they enjoy the freshness of the produce, the personal contact is a refreshing fringe benefit.

"Thank you," says a pin-stripe-type mechanically to Brinton Ramsey, 20, a strawberry blond sunbleached to her platinum eyelashes. "You're welcome," she says warmly, and he looks back, hesitates and smiles. "Thanks," he says again.