Open for dinner daily 6 p.m. to 10 p.m., for brunch 11:30 a.m. to 2:30 p.m. Sunday. AE, CB, D, MC, V. Reservations. Prices: At dinner appetizers $5 to $7.50, main courses $12.50 to $19.50. Full dinner with wine, tax and tip more than $35 a person. Sunday champagne brunch $16.50 a person plus tax and tip.

This is the largest convention hotel in the East," the maitre d'hotel at the Sheraton Washington's Americus restaurant is fond of saying.

And that is probably what is wrong with the restaurant, which otherwise appears to have been born with a solid gold spoon in its mouth. It looks like a fantasy realized, but as usual the reality falls a little short of the imagination. The room is a glassed-in balcony overlooking the treetops of the Sheraton Washington lobby; unfortunately, instead of the waterfall such a setting suggests, the focal point is two escalators.

But inside the room the glamor is intact. Tables are hewn from burled wood, set with hand-woven linen mats and napkins in handsome rings that the captain whisks away as he sweeps the napkin into your lap. (One shudders to think how many of those elegant napkin rings must have disappeared by now.) A spotlight hangs low over the table, reflected in a crystal-clear obelisk that serves as centerpiece. The softly upholstered chairs bounce slightly as you settle in; the velvety rust carpeting cushions your feet. The pianist in black tie bids you to make a request. A busboy pours Saratoga water into your glass and delivers a basket of homemade breads-- whole wheat, dill, nut--which could have been sufficient reward for Little Red Riding Hood's grandma. The menus are covered in raw silk, their pages textured paper of weighty luxury. Even the matchbooks are uniquely extravagant.

This restaurant celebrates America in its native foods and pioneer spirit. No prosciutto here--instead, Smithfield ham. No seviche, but pickled conch. The fish are not French turbot or English sole, but all-American red snapper and crayfish and pompano. And instead of imported snails as an appetizer, those indented plates are the platform for slices of chicken breast wrapped around oysters, green peppers, ham and mushrooms, then sauced with a light and aromatic sour cream butter.

The pioneering is in serving the prime rib lightly smoked, as well as the rack of lamb and the boneless duck. And these inventive touches make choosing difficult. The 16 main courses buffet you between the temptations of salmon topped with vegetables and baked in phyllo dough or of crayfish-- fresh, the waiter says--with shrimp and creole rice. Perhaps red snapper with lump crab meat and shrimp: no, once the waiter reveals it is Alaskan king crab--therefore frozen--one can readily pass on that. (Why not blue crab, which is generally what is meant by lump crab meat?) But lobster baked with lobster stuffing and scallops increases the indecision. That's without even turning to the meats: breast of chicken with ham, banana and coconut; capon with cornbread and oyster stuffing; rabbit or venison or pheasant, Americanized with cranberries, barley, apples and walnuts in the stuffing. The prices are high: $19.50 for a porterhouse steak, $18 for veal chop or rack of lamb, $17.50 for prime rib and down to $12.50 for the capon. But this food sounds like an experience.

Occasionally it is. The waiter promised the second-best seafood chowder in the world, and I wouldn't quarrel if he called this creamy ivory soup the best of all. And the appetizer of oysters and chicken breast is delicious. The cold seafood appetizer is a gorgeous still life, garnished with an American touch of alfalfa sprouts and presented with tiny cups of three sauces, though the seafoods were a bit shopworn. And among main courses, the pompano is impressively fresh and lightly moistened with an herbed cream sauce, topped with slices of smooth scallops and firm mushrooms.

But the shining lights of the menu, the smoked meats, fizzle out. The lamb is so soft it seems unlike meat, perhaps from being cooked at a low heat so long that it remains rare but loses its texture. The prime rib, too, is rare but juiceless. Boneless duck is worst of all, being fatty and soggy and covered with an unpleasant thick brown sauce. In none of them does the smokiness add more than a tongue-stopping, not particularly appropriate surprise. But none is as dismal as the venison, marinated so long that it tastes like sauerbraten, slathered with a candylike cranberry game sauce.

The kitchen repeatedly tries to be glamorous. Tomato cups are filled with broccoli florets, baby ears of corn, batons of carrot. But the tomato looks and tastes like wax, as if the kitchen exercised no judgment over the produce it accepted. Potato puffs are an ambitious undertaking but here are too heavy to have been worth the trouble. As for desserts, the fudge cake is the safest; cheesecake was crumbly and oversweetened, pecan pie lacked crunch and flavor, and the Americus dessert of orange mousse on a meringue shell, with what seemed to be canned mandarin oranges, was like something out of a gelatin-tricks cookbook. And although Americus has built an extensive list of American wines, at such high prices one would want to know the vintages.

Sunday brunch at Americus is a sight to be seen (if not necessarily a meal to be eaten). The buffet table stretches in two directions, one side being the "breakfast items" of salads galore, smoked and pickled fish, seafoods in tart shells, blintzes, french toast, chicken livers (the best of the lot), eggs benedict with pork patties instead of Canadian bacon, egg- filled croissants and breakfast meats.

You're only halfway there. You still have the table of "lunch items," the bluefish with salmon mousse in puff pastry, chicken breasts stuffed with wild rice and whole cranberries, double-thick lamb chops in a minted fruit sauce, New York strip sliced to order with two sauces, p.at,es, cold beef Wellington. And more salads. And a dessert buffet, its center like an immense wedding cake.

It looks spectacular. Cold dishes are arranged on mirrors, and the tables are watched over by tallow pandas. A treasure chest with a pineapple-skin veneer has straps of grapes and is filled with banana-headed birds. The world--and certainly this city--rarely sees a more elaborate display of food. And surely among such an array there are wonderful things to eat: hand-cut smoked salmon, some lively salads, fruits right out of the tropics, excellent rare beef.

But it takes a lot of wading through greasy croissants, steam-table-massacred fish in pastry, dried-out chicken or smoked fish, limp vegetables, french toast that absorbed so much butter you could squeeze it out. And even the thick, juicy, rare lamb chops can only be appreciated once you have scraped off their sweet sauce. The basic ingredients seem of high quality, but they have gone through too much between the larder and the plate: overseasoning, overcooking, resting too long on the steam table. Even the fresh orange juice tastes bitter, though it improves the yeasty, bland champagne that is poured freely during the brunch.

A lot of effort goes into the food at Americus. But in this case the whole is less than the sum of its parts. TURNING TABLESBy Phyllis C. Richman and Carole Sugarman Washington Post Staff Writer

Idea of the Week--We're all familiar with the waiters' routine of offering a taste of wine for your evaluation. Wouldn't it be nice if he fed you a forkful of your entree for acceptance, too?