WASHINGTON finally has a first-rate French restaurant. It's the old country store that's been converted into the Inn at "Little Washington" - Washington, Virginia, 90 miles and easily a century or two away from that big Washington on the Potomac.

City people make certain assumptions about French country inns, assumptions that have to do with one-room-school-house educations and lack of urban resources. While it's true that Rappahannock County is not directly on the truffle route, running a Frech restaurant there - or any restaurant - has certain advantages if you know how to use them.

The Inn has the advantages of youth, namely two young owners with enough drive and energy to get themselves to Washington, D.C., for the day's softshell crabs and to turn out 10 different desserts from scratch of an evening. (I can personally vouch for four of the five tarts, three frozen desserts, the coeur a la creme , the creme au chocolate and the creme fraiche , having had the energy to taste every one of them myself of an evening). They have the energy to dip mint leaves in chocolate to garnish a dessert, to organize a list of 11 aperitif wines to compensate for lacking a liquor license (nobody has even applied for a liquor license in the country before). They have the patience to price their nicely balanced list of French and California wines reasonably and to wait for their coffers to fill in due time.

And they have enough good sense to turn their country location to advantage. Neighbors bring them flowers wear more spectacular flower arrangements than any city restaurant could afford. In lilac time the restaurant is a pale lavender bower. Later in spring, the tables wear silver bowls of spiky purple scallion blossoms with sprays of mint leaves and soft irises. In season, fresh herbs arrive at the back door and then on your plate of scampi pescadora - sauteed in a light batter with garlic and parsley, and ringed with a delicate fresh tomato sauce. A nearby trout farm becomes the source for fresh rainbow trout amandine - moist and sweet and buttery.

As one would expect, the vegetables are fresh - from the surprise crunch of chopped raw watercress in a chicken-based cream of watercress soup to pimento-ribboned asparagus vinaigrette . Any day, wild strawberries and pears among the desserts displayed on the fire-enfine-red woodburning stove that serves as a sideboard.

It is a piquant balance, the sophistaction of a seven-foot gilded mirror with the ingenuous touch of hanging lamps of baskets, the tall white candles on polished cherrywood tables with paper doily placemats. The dining room looks part manse, part tearoom. The service is well rehearsed, knowledgeable, smooth - though the kitchen may slow at midmeal.

The city-country balance carries through the menu. Kiwi fruits - all the rage of Paris - are wrapped around local country ham and served with a lemony whipped cream sauce as an appetizer. The sherbet to cleanse the palate between courses is pineapple, and homemade, as is the down-home strawbeerry ice cream. Main dishes number fewer than 10, and are fairly simple, from roast duck to tournedos, but there's an imaginative touch to each: marsala sauce on the duck, perhaps, or roquefort on the beef. While the quality is high, the dishes often exciting, there are lapses - dark veal in a too-thick sauce one day. The tarts are exquisitely perfumed, but their puff pastry cases sometimes miss sufficient browning. A roquefort dressing on the salad has been too heavy and too pervasive, a rice pilaf excessively herbed. But one is hard-pressed to remember such flaws in a meal that wends its way from homemade breads with herbed butter through aspic-glazed mousse of duck liver to impeccable softshell crabs and pastries so stunning that you order them all.

The prices also have a country touch, the main dishes averaging $8, appetizers $1.35 to $2.95, desserts less than $1.50. Not cheap, but probably $10 less than a similar multicourse meal in Big Washington.

Washington, Virginia, is, of course, a long way to go for a meal. And until the Inn refurbishes its upstairs rooms for lodgers, the only place to stay in town is the Lake Motel, a deceptively charming stone building on a lawn of weeping willows, with schoolhouse-green cinderblock rooms that one child described as "looking like bathrooms."

The town, however, has charm that survives a day of investigation, its street signs carved in wood - even the one that reads "Bank Customer Parking Only." It's a town of white picket fences and plastic geraniums, antique shops and a recycling center. Surveyed by George Washington himself in 1749, it has changed as little as possible since then. Peter Kramer still makes furniture as if he were doing it in the 18th century. The Rush River Company, a crafts cooperative of eight artisans, serves ice-cold cider, peanuts and pretzels among the split-oak baskets, patchwork skirts and banners, pottery and ironwork and woodwork. It also sells antique tools and calicos to supply other budding artisans. A stroll down the town's streets goes past antiques shops and the courthouse; a short drive takes you to a Christmas tree farm and orchards where you can pick your own apples. Farther afield is Sperryville, where the antique shops are bigger and more commercial, with a few more eating places of less character.

But there is a less public - or semipublic -Rappahannock County. Call Ruby Jenkins in "Little Washington" (703/675-3352) and ask her to open her First Washington Musuem for you. An 18th-century kitchen and one-room school were furnished from her lifelong collection, and in the rear is a kind of museum to the museum as well as to the town. Or make an appointment with Flossie Williamson at Oak Forest Garden in Woodville (703/987-8347) to see her herb garden and buy a few plants or a soup posy or a fragnant herb moth repellent. Be sure to leave enough time in case Mrs. Williamson invites you for herb tea.

Then, if you haven't reserved yet another meal at the Inn, try to arrange with Nestor Sampson at the Teepee (703/987-8188) in Sperryville to make you an Oriental meal of fire beef or fried noodles and wontons with hollowed-out cucumbers stuffed with bamboo shoots and dried mushrooms. Most of his menu is the all-too-familiar hamburger and frozen fried seafood conglomeration. But those who care about such things know to order his cold plate of homemade chicken salad, potato salad and coleslaw, or make sure there is something Oriental among the specials, to turn the knotty-pine highway luncheonette into an Eating Opportunity.

If you hit Rappanhannock County on a lucky weekend, you'll find a chicken barbecue in the schoolhouse or a dance concert, a furniture exhibition by Peter Kramer or an herb show by Flossie Williamson. But in general there's not a lot going on, and it's meant to be that way. A couple of visiting city kids schemed about where a skateboard park might fit. Not a chance. The biggest crowd between Amissville and Sperryville was a group of four gathered around a phone booth. "Little Washington" will never be mistaken for Big Washington, even with a French restaurant.