WHEN THE politicians return to this city from the hustings late this fall, they are going to find a dramatic change in the gastronomic face of Washington. There are those who will be tempted to say it would be a surprise to find a gastronomic face of any sort, but they are out of step with the times. While the restaurant explosion of the past two decades continues, it is rapidly being overtaken by a demand for esoteric and costly foods and food products to serve in the home.

Food retailers such as the French Market and several wine and cheese shops have stocked so-called gourmet food items for some time. More recently, the Georgetown Wine & Food Company introduced a selection of high-quality American products, and Pasta Inc. capitalized on the rapidly spreading addiction to fresh pasta. There are some interesting shops in the suburbs as well, but in the District itself the following retail food enterprises are on the fall menu.

Market House in Georgetown: The historic building facing the intersection of Potomac Avenue and M Street will have an opening celebration Sept. 6. Already, though, 15 of the 18 shops are functioning. They range from Lumps Que, a barbecue specialist, to Fresh Daily (elegant snacks or complete meals from Lansdowne Caterers). Prepared kosher dishes, as well as Chinese, Japanese and Italian specialties are being sold as fast-food to eat there or take out. Meats, produce, baked goods, coffee, candies, the Crabtree & Evelyn specialties, ice cream are sold at separate stalls within the building. The Cannon's Seafood stall is not yet open, and in late fall the Pronto chain will open a pasta restaurant on the market's lower level.

The American Cafe: A handsome tile and wood second-floor market has opened above the restaurant, 1211 Wisconsin Ave. It offers a stylish variety of foods to take home and will cater dinners or parties. On display are salads and meats from the restaurant's kitchens as well as cheeses, vegetable pates, Citterio sausage meats, Oregon fruits, various breads, bottled waters and ciders.

French Bread Factory: A bakery and pastry shop in the new Prospect Place complex 3222 N St. NW. A wide range of dessert items from the French repertory are on display in this oddly shaped shop and one may order bread sculptures by baker Jackie Babonneau. Breads, croissants and rolls are freshly baked. There are several tables in the adjacent courtyard for outdoor noshing.

All these are serving the public now. Still to come:

Your Watergate Chef: A shop within the Watergate featuring foods from the kitchens of the complex's three restaurants as well as imported specialty products used by the chefs of the restaurants. There will be a sandwich counter and "old-fashioned" soda fountain that will prepare, among other delicacies, authentic egg creams.

Suzanne: A "gourmet deli" or "fancy food carryout" that will open in mid-October at 1735 Connecticut Ave., next to Larimer's. New York City's much admired specialty store Dean & DeLuca will provide some of the merchandise and Carol Mason, a leading [TEXT OMITTED FROM SOURCE] and cooking [TEXT OMITTED FROM SOURCE] kitchen. Prepared dishes to be reheated at home and salads will be sold, along with charcuterie, an extensive selection of cheeses and pasta. A wine pub located above the shop will present a limited selection of the foods.

Williams-Sonoma: The trendsetter in upscale cookware stores, this California based company will open a large facility in the Mazza Gallerie on Wisconsin near Western Avenue in mid-October. A series of special events is planned for the week of Oct. 20. In addition to a broad selection of cooking equipment, the store will stock specialty foods and condiments previously offered through the Williams-Sonoma catalog.

In sum, there promises to be a great deal of sampling and tasting going on this fall and some lively competition among purveyors of tastes. There is a danger, too. With so many new items for food fanciers to choose among, it may be possible to eat one's way through the upcoming dinner party season without tasting [TEXT OMITTED FROM SOURCE] made from scratch.