727 15th St. NW. 783-0166

Open Monday through Friday for breakfast from 7:30 a.m.,

Monday through Friday for lunch from 11:30 a.m.; Monday through Thursday for dinner from 5 p.m. to 10:30, Friday and Saturday from 5 p.m. to 11:30. Closed Sunday. Reservations suggested. AE, MC, V, Choice. Valet parking evenings. Prices: Appetizers $4 to $5, lunch entrees $6.50 to $12, dinner entrees $9.50 to $17. Full dinner with wine, tax and tip about $40 a person.

A FEW YEARS ago you could find every kind of cooking in Washington but American. Now the Nation's Capital is becoming a showcase of the country's culinary resources. And while we don't yet have a great influx of traditional or regional American cooking, we do have New American cooking to show off to foreign visitors as well as to try ourselves.

The newest of the New American, Prime Plus, is even more welcome for its adventurous location at the edge of the reviving downtown, just where the city needs more good restaurants. Its facade is sheer grandeur -- one of Washington's great long-gone movie theaters -- but the entrance is hard to spot, only a small sign pointing to the downstairs dining room.

If the restaurant itself is a surprise in that location, its interior is a second wave of surprises. A small dining room is carved into even smaller cubicles of one or two tables, suited for intimate dinners or conversational lunches. Between the cubicles there are half-walls of glass bricks to let in light. The colors are luscious -- raspberry mousse and pearly gray. The fabrics are luxurious -- silk banquettes and Lucite-covered wood tables. And the designs are handsome -- Art Deco sconces, recessed ceiling lights and geometric-print fabrics.

In the New American style, emphasizing the freshest of the season, Prime Plus changes its menu twice a day, with about eight to 10 appetizers and a similar number of main dishes, including complex salads with meat or seafood to qualify them as main courses. The plates are beautifully garnished still-lifes. But some of the food is high art in the eating as well as in the arranging. This is an experimental collection of dishes: On a warm-weather menu we found veal scallops with chanterelles, bacon and port; New York strip steak with pinot noir butter; tuna carpaccio with almond oil, lime juice and avocado; cream of sweet yellow pepper soup, and chilled asparagus soup with vodka and salmon caviar.

Appetizers have been uncommonly good. One evening waffles had been made with crab and dill in the batter, then garnished with crr. They opened new and delicious possibilities for waffles. Shrimp have been marinated in vodka and grilled to a smoky juiciness, garnished with starfruit. Another day they were just as delectably sauced with corn and jalapenos. Then shrimp and corn were served as a soup, fresh flavored and with a homey dice of potatoes and carrots. Another interesting and successful soup was ham and arugula, thick with greens and with cream. Then there are the variations on a mushroom theme: fresh baby artichokes and oyster mushrooms on toasted french bread with a dab of golden cream sauce; or chanterelles in puff pastry with a slightly sweet sherry and leek sauce. In all, the appetizers have been intriguing and suavely executed.

Where things have gone wrong were the main dishes. One day a salad sampler included a wild rice and seafood m,elange drenched and soggy from its dressing -- perhaps it had sat a day too long -- and a dried-out, tasteless mixture of ham, nuts and bow-tie noodles. Another day the wild rice salad was crunchy in texture and sprightly in flavor, well balanced and fresh tasting.

Meat dishes have disappointed, from a grilled duck breast with sage and cabernet sauvignon sauce that was dry and dull, to a grilled chicken with honey and basil that had lost its succulence in a few moments' overcooking, to a grilled pork with ginger port sauce that was even more dry and devoid of liveliness.

Fish has fared batter. There has been a saut,eed salmon fillet with lightly cooked fresh tomatoes -- a vivid contrast in coral and red -- topped with briny, crunchy green sea beans. Timbales of crab mousse wrapped in green leek leaves were also a pretty color contrast and rather good, though short of the excitement of the first courses.

On every plate there is something to like. With the pork it was a fluffy pale orange potato souffl,e. Many dishes are accompanied by bright and crisp julienned carrots and snow peas. The salmon came not only with green beans and carrots, but also with a

homey, delicious mound of

kasha. The rolls, dark ones

sometimes studded with

walnuts, are served with

tiny scoops of tomato-mint

butter, which may be slipping over the edge of cuteness, but show how hard

the kitchen is trying.

The wine list is small

and not what you might

choose if there were more possibilities presented, but prices are admirably low, with most of the bottles $11 to $15 -- surprising in such an elegant restaurant. Half-bottles and several wines by the glass are also available.

Desserts can be highlights at Prime Plus. There has been a nutted chocolate terrine as rich as fudge, on an intense raspberry pur,ee; and raspberries topped with a souffl,eed custard and brown sugar, then browned for a hot gratin. The best dessert I've tasted was a pie of macadamia nuts, chocolate chips and Tia Maria in a flaky and buttery crust. Apple pie needed less salt in its crust but had the proper tartness in its filling, and chocolate sour cream cake was everyday stuff. A mocha mousse tasted like old frosting; perhaps its trouble, like the salads', was that it had sat around too long.

The service, like the kitchen, seems very concerned and enthusiastic but a little awkward. With enough experience and some reinforcement for what it does well, Prime Plus could be the kind of sophisticated downtown restaurant that in itself helps to revive downtown.