Open Monday through Friday, 11:30 a.m. to midnight; Saturday, 6 p.m. to midnight. Reservations. AE, MC, V. Prices: At lunch, entrees about $4.50 to $10.50. At dinner, appetizers about $2 to $5, main dishes about $10 to $14, desserts about $2 to $3. Full dinner with wine, tax and tip about $30 to $35 a person.

he "happy hour" verges on an all-night sing-along, the thousand-of-a-kind office building interior has managed a Manhattan look, and the kitchen is volubly French. Cheval Rouge is indeed a surprise in the concrete plains of Tysons Corner.

You wouldn't know there is anything unusual going on in the Tycon II building except for the red neon horse in the window and the covered dining patio. Then, once inside this routine-looking office building, you find a door that has a blackboard listing refreshingly nonstandard dinner specials: broccoli or cucumber soup, scallops with caviar, duck with peaches or pears. The office world recedes further when inside the door the greeting is warm and the bar action is lively.

Beyond is a dining room, long and narrow, bordered by lacy modern draperies and stripes of wood and mirror. The chairs are basket-woven, bouncy with thick cocoa-colored leather cushions--comfort in a clean and glassy environment. The walls are decorated only with outsize and luscious photographs of food.

It is all very refreshing, a feeling enhanced by the choice of aperitifs. There is champagne by the glass and a kir royale-- champagne and cassis, a pretty thing though likely to be made too sweet if you don't suggest otherwise. The wine list has a choice of three house wines: American, Italian and French. The rest of the wine list is smallish but far-reaching, with seesaw prices that suggest careful culling before you order.

The same is true of the menu. One of the problems with Le Cheval Rouge is its cockiness in raising prices. Were the main courses still an average of $10 as they were on the first menu I saw, I would feel more forgiving; but my last dinner for two cost only $5 to $10 less than dinner with an equivalently priced wine has cost recently at Le Lion d'Or. So Le Cheval Rouge has priced itself into tough competition.

The best of its appetizers have been soups. Cream of mushroom and cream of broccoli have been delicate, creamy but not heavy, tasting clearly of their vegetable but still subtle. And a cold cucumber soup has managed to avoid the blandness such concoctions often fall prey to. Not so with the pates, though. They have been dull and characterless, their main asset being the generosity of the portion. One day the,e was so salty it could have passed as ham,e. Gravlax, too, has been saltier than that marinated salmon needs to be, and too oily and thickly cut. Otherwise, the standing hors d'oeuvres include nothing more original than snails, mussels in garlic butter, melon with prosciutto, clams casino and hearts of palm, plus several soups.

Main dishes are less easy to predict; they have ranged from very good to drab, but weighted toward the ordinary. To start with the best, duck is a dish rarely done well in any but a Chinese restaurant. Ordinarily cooked ahead, it is so often wrecked in the reheating that ordering it is like playing Russian roulette with five bullets. Yet at Le Cheval Rouge it came moist and fat-free, the flavor full and gamy, the skin crisp. We could have had it with a garnish of beautifully fanned-out peaches, but they were canned, so we chose the duck with cassis and were rewarded with a hail of tart and plump black currants that made this a delicious dish. Sea scallops with caviar were a daily special, and another pleasant dish, though the caviar was that inexpensive and garishly colored grocery-store stuff. It was not a particularly refined dish, but the scallops were nicely cooked and the combination certainly tasted good. Another special, rack of lamb, is about as easy a preparation as a kitchen could choose, but these eight tiny ribs were juiceless, soft and bland, well trimmed but lacking every other endearment--all for $15.50.

The standing menu is small and routine: trout bretonne, scallops provencale, red snapper with beurre blanc, sole dieppoise, veal francaise or normande, pepper steak, tournedos and coq au vin. My samples would not lead me again beyond the duck. Red snapper had a stiff texture, and its taste lacked the satisfying sweetness of truly fresh fish. Pepper steak was rare as requested, but lacked the flavor rendered by proper searing, and the creamy sauce fell flat except for the intermittent bite of the green peppercorns.

This is a kitchen that tries hard in some ways, but then slips in important details. One evening veal Oscar was not only a daily special, but the waiter's strong recommendation. The veal itself was worthy of his regard; it was neither cut too thin nor pounded too much, so it had kept a nice springiness. And the asparagus that topped it was fresh, but so overcooked that the touch of a fork rendered it mush, and it was watery so that it diluted the hollandaise and the brown sauce under the veal. On top were batons of king crab that were as soft as baby food but twice as tasteless. A m,elange of overcooked and watery summer squash and green beans on the plate further watered down the sauces, so one wanted to remove the veal, dry it off and enjoy it alone, and then fill up on the decent potato puffs--a bit doughy but not greasy--that had escaped the flood.

Don't stick around for dessert if you are going to meander beyond the strawberries with sabayon sauce, which are quite good. If some of the best restaurants around can't make a decent berry tart, what can you expect from this adequate but far from thrilling kitchen? Stolid, chewy tarts, of course. But even the most mediocre restaurant should be able to make an acceptable chocolate mousse; at Le Cheval Rouge it was gritty with undissolved sugar. The waiter, when told, shrugged.

Le Cheval Rouge is a pleasant getaway in the maddening stretch called Tysons Corner. People at the bar were obviously having fun, and could choose from a nice variety of bar food from snails to cheese platters to pate sandwiches or hamburgers, from early evening until late at night. Furthermore, in a neighborhood without French restaurants, this is a reasonably professional one. You can get a good meal at Le Cheval Rouge, and spend a relaxing evening. Just don't mistake it, because of its prices, for a major French restaurant.