(FORTUNE Magazine) – Stock and bond traders eat tuna sandwiches at their desks, and bigwigs swear by their firms' private dining rooms. For other hungry Wall Streeters and visitors from around the world, lunchtime has long meant a choice between settling for inferior food or blowing part of the day on a trip out of the * district. But today the square mile of Manhattan below Chambers Street is fast becoming a rewarding midday venue. Lunchtime in Wall Street has its own style. Most restaurants are jammed with customers belly to belly, especially when stock market activity is slow. The atmosphere is usually small-town clubby; men outnumber women by as much as 10 to 1. French, Continental, and American fare predominate, but whatever the cuisine the portions tend to be big. Wall Street goes out to lunch around noon, and by 1:30 P.M. the heavy crowds are gone -- along with most of the daily specials. The prices for the restaurants listed include appetizer, entree, dessert, a drink, and wine. All accept major credit cards; unless otherwise noted, they also take reservations, which are a good idea at busy hours. Most are also open for dinner. One of New York's most famed restaurants in the early 19th century, Delmonico's had nothing going for it by the time it closed in 1977 but the distinctive building it occupied at 56 Beaver Street. The new owners who reopened it three years ago have restored the faded glory to decor, service, and food. Beads of red caviar amid the fresh bay scallops blitz the taste buds with bursts of flavor. Mixed Grille Delmonico is assembled from lamb and pork chops, filet mignon, liver, and bacon, each individually cooked to order. A dessert called bittersweet chocolate, a dense bar covered with vanilla sauce, is sinfully good. The tab for two: $110. Telephone: 212-422-4747. The tables are widely spaced, the service smoothly efficient, and the food first rate at Brasserie Montparnasse, 44 Beaver Street. The proprietors call their cooking moderne cuisine, which means light sauces and crisp vegetables but plenty on the plate. Try saddle cuts of baby lamb stuffed with herbs and served with fresh artichoke hearts. For dessert order strawberries and kiwi fruit on a flaky crust. Cost for two: $60 (344-9160). The plain doorway to Rincon de Espatna at 82 Beaver Street is uninviting. But press on through the nondescript entryway and past the bleak barroom. In a small dining room at the back you will find hearty, authentic Spanish dishes such as paella valenciana and fillets of pork barbecued with almond sauce. The salad and desserts, however, are as undistinguished as the surroundings. Cost for two: $57 (344-5228). The owners have another restaurant of the same name in Greenwich Village. DURING THE BEAR YEARS of midday dining, many Wall Streeters counted on Harry's to get them through a day well fed. There now are three Harry'ses. Harry Poulakakos, the original Harry, runs two, at 1 Hanover Square (425-3412) and in the Woolworth Building at 233 Broadway (513-0455). The food at both is hearty: salmon steak in lemon sauce, prime ribs, and a weekly special of well-executed Beef Wellington (Wednesdays at Hanover Square, Thursdays at the Woolworth Building). Cost for two: $52. A third Harry's, at the American Stock Exchange, is now in other hands; it remains a good copy of the others, with comparable prices (732-8736). Sweet's, on the second floor at 2 Fulton Street, was another standby during leaner times, serving some of the best fish in the city in austere surroundings. The building has been completely made over as part of the South Street Seaport restoration; the fish is still fresh, but the old, slightly seedy magic is gone, and new competitors give you more for the price. Tab for two, including a la carte entrees: $46 (344-9189). More of interest to history buffs than gastronomes in recent years, the comfortable 18th-century Fraunces Tavern at 54 Pearl Street has tried to upgrade its kitchen. The results are sometimes strained; for example, an otherwise excellent dish of tortellini with king crab meat and baby shrimp arrived peppered with bits of bacon. Safer is the simpler American fare, such as boneless breast of chicken sauteed with mushrooms, onions, shallots, and fresh thyme. The ''triple XXX'' chocolate mousse is glucose heaven. Cost for two: $62 (269-0144). Japanese bankers and traders pack into Mikaku, 67 Liberty Street, many in such an apparent rush that they consume their whiskey, cigarettes, and food simultaneously. The restaurant has a good sushi bar, but the most popular dishes are based on udon, a Japanese noodle. Mikaku serves it either in a broth with shrimp or chicken or cold, as a side dish, in a delicious sauce made of mayonnaise, mustard, vinegar, and a pinch of minced vegetables. Cost for two: $36 (349-0060). La Tour D'Or occupies J. P. Morgan Jr.'s old apartment on the 31st floor at 14 Wall Street. The French menu boasts some good dishes. Among these is a tender duck, Le Canard de la Semaine, which may come with a pear sauce one week, a strawberry or kiwi sauce the next. But a putatively fresh fillet of sole was so mealy it could have been frozen, and the service can be uneven. Cost for two: $80 (233-2780).

GLOBED CHANDELIERS and elaborate wallpaper embellish the mockVictorian dining rooms of St. Maggie's Cafe; the food is meticulously prepared. Melt-in- your-mouth roast fillet of beef comes with a brandied peppercorn sauce based on a rich veal stock; the fresh Maryland crabmeat appetizer is presented on endive leaves with a distinctive beet and horseradish sauce. Cost for two: $50 (943-9050). Principal owner William Galvin also runs St. Charlie's Restaurant at 4 Albany Street near the American Stock Exchange, with similar food and decor (964-6940). Mayor Edward I. Koch and his retinue eat often in the Bridge Cafe at 279 Water Street, hard by the Brooklyn Bridge, but most of the lunchtime crowd are Wall Streeters. A seedy waterfront dive in earlier times, the one-room bar and restaurant has only 15 tables (not counting the one always reserved for Hizzoner). It does not take reservations, so come early or late if you can't stand waiting. The eclectic menu, which changes daily, offers such dishes as fresh flounder meuniere with shallots and roast chicken with lemon and coriander. In addition to offering a lengthy wine list, the restaurant serves a half-dozen good wines by the glass. Desserts, made at home by two freelance bakers, are mouthwatering; try bourbon and pecan pie. Cost for two: $40 (227-3344). From the southernmost reaches of the district the Bridge Cafe is a ten-minute cab ride or a 15-to 20-minute walk -- and worth the effort.