Open daily, 11:30 a.m. to 3:30 p.m. and 5:30 p.m. to midnight. AE, D, MC, V. Reservations recommended. Prices: Lunch main courses $4.95 to $8.95; dinner main courses $7.50 to $13.25; supper main courses $5.25 to $9.95. Three-course dinner with wine, tax and tip about $25 to $30 a person.

A couple sat on a ruby velvet banquette, silvery service plates before them on the white tablecloth, massive crystal chandeliers overhead reflected like stars in the windows. The waiter, in a short, fitted crimson jacket, took their drink order and described the evening's special, swardfish in wine sauce. Their martinis arrived. Their salad, crisp quarters of romaine and peeled tomato wedges drizzled with creamy curry dressing, followed, then their swordfish, with fresh vegetables spooned by the waiter, French-style. The second martini they requested accompanied the meal. They received the check, paid and left. It all took less than a half hour.

The Roof Terrace knows how to send you off to the theater quickly but without panic. That couple had their drinks, salad and main course within five minutes of being seated, and the rest of the half hour was leisurely eating. With an hour and a half, as the restaurant recommends for pre-theater dining, they know how to let you linger just enough over an aperitif, serve you three courses and coffee, then send you on your way in time for the curtain. It is a smooth performance. If you are not meeting a curtain, however, you would do best to avoid the theater rush, for theatergoers rightfully get priority service.

The Roof Terrace last year came under the management of New York's Restaurant Associates, who since then have made progressive innovations in menu and service. Fortunately, they left the room substantially the same. It looks cleaner and more brilliant than it has since its early days, and its pale gold and ivory brocade walls, plush ruby upholstery and carpet, mirrors reflecting the windows' view of monumental Washington are left uncluttered except by modest flowers and opulent pastry displays. The ceilings are breathtakingly high, the tables spaced with abandon for real estate costs, and the high-backed banquettes some of the most seductive dining arrangements in town.

While the environmental improvements have been subtle, the improvements in service are blatant. The captains are polished is discussing the menue, serving (if not necessarily understanding) the wine, boning the fish. They are personable, having the wit to save the situation when, for example, a waiter presents only two pastries as if they are the entire choice, though the patron has seen 10 more on the pastry cart. In the cocktail lounge, which serves hors d'oeuvers substantial enough to substitute for a meal if necessary , the waitresses are attentive without being intrusive, partly responsible for the lounge's becoming one of the most comfortable places in Washington for drink and conversation.

So two sides of the dining triangle, environment and service, have been set straight. The Third, the food, wavers considerably. The Roof Terrace dinner menu is well designed to cater to a variety of tastes with dishes that can be finished in a hurry for theatergoers. For steak-and-potatoes diners there are prime ribs, filet mignon, steak with herbed butter, rack of lamb, liver with onions and mixed grill. Fish eaters have Dover sole amandine, a daily fresh fish choice and veal cutlets sauteed in a batter of eggs and parmeasan. For those with a taste for the unusual, the choice includes breast of chicken stuffed with spinach, feta, dill and sesame seeds, or duck with wine and peppercorn sauce. Three cold platters are available: smoked Cornish hen, king crabmeat salad, and smoked salmon with shrimp salad.

Nearly everything, unfortunately, sounds more appealing than it tastes. The roast beef, large and rare, lacked juiciness and flavor. Breast of chicken sounded succulent but tasted dry, all those wonderful stuffing ingredients adding up to little and its lemony sauce tasting like mock hollandaise. The duck was a mess of soft, soggy stewy meat in a floury thick sauce slightly peppered. And the fish of the day one day was lobster tails, touted as large and fresh; the small tails that were served tasted like the usual frozen lobster tails. The Dover sole was decent fish acceptably cooked, and one main dish -- mixed grill -- was excellent, an assortment of good meats from pale, thin veal to thick, delicate calf's liver with lamb chop, bacon and thin beef filet, all carefully grilled and garnished with those wonderful lacy fried potato slices called gaufrettee potatoes.

In other words, plain seemed best. While appetizers were almost universal disappointments -- unripe melon, kiwi fruits with inferior prosciutto, chopped liver on a brioche that had the texture of oyster crackers, and oysters with caviar and sour cream that needed something to bring the flaccid oysters back to life -- soups were satisfying, both the rich, smooth onion and the tangy cold orange tomato bisque. And the rest of the culinary trappings had appeal. The basket of rolls includes fragile corn sticks, a little too sweet but nevertheless fine. And the vegetables show attention, from the bright, crisp broccoli to the baked potatoes -- without foil -- sprinkled with coarse salt before cooking. The salad is crackling fresh, though the dressings could use some further attention.

A one-page wine list is a shallow listing, which would be suitable if the prices were more modest. Even Blue Nun, for goodness' sake, is $12.50. One good choice is Fretzer '77 gamay beaujolais at $10.

The kitchen's major effort seems to focus on desserts; each night the pastry cart is layered with a dozen different cakes and tarts, elaborate ones like gateau St. Honore and Sacher torte. Best of the lot I tasted one night were chocolate mousse cake and chocolate concorde, decorated with rolls of chocolate meringue; both were rich with chocolate, creamy and elegant. Another night, though, the dense chocolate Sacher torte was dismal, a damp and tasteless gray-brown mass with waxy glaze. The hazelnut torte and Linzer torte, though insufficiently endowed with butter, were wel-flavored with nuts and beautifully composed. Zuppa inglese was creamy and sumptuous. As for the fruit tarts, they are better to look at than to eat.

This is a restaurant of grandeur, with prices to match. Main dishes average $12, appetizers $4 and pastries $3 at dinner. Hors d'oeuvers in the lounge, more inventive than excellent (order the skewered meats or the fried shrimp but expect a sugar jolt from their sauces), average $4.Those are not outlandish prices, considering the surroundings and the service, but the food is anonymous, little of it notably good or bad. The concepts outshine the renditions.

What is worse, the coffee won't keep you up during the show.