Start with your favorite Italian restaurant and work backward. Find out where the restaurateur gets sausage and fresh mozzarella. Many Washington restaurants rely on ma-and-pa Italian markets, such as Vignola Pasta Gourmet. Once partners at Italia Delicatessen in Silver Spring, Arturo and Alma Vignola now turn out their own homemade Italian sausages, whole-milk mozzarella, florentine quiches and pizza rusticas, antipasto platters, fresh pastas and main courses such as veal with white sauce and eggplant parmigiana. De Cecco pasta is at its cheapest here -- $1 a one-pound box -- and fresh pasta is $1.50 a pound.

Vignola Pasta Gourmet, 113-A N. Washington St., Rockville. 340-2350. Other sources: Litteri's, 517 Morse St. NE. 544- 0183. Italia Delicatessen, 8662 Colesville Rd., Silver Spring. 588 The Italian Store, 3123 Lee Hwy., Arlington. 528-6266. Italian Gourmet, 505 Maple Ave. West, Vienna. 938-4141. GREEK

The task of making delicate butter-and-cheese-filled Greek spanakopita is not for the nervous hostess. But the flaky, bite-size pastries are delicious. St. George Greek Orthodox Church makes a business of homemade Greek delicacies. With one week's notice, you can order 12-by-20-inch trays of moussaka and baklava for $32 or spanakopita for $28. A box of 36 bite-size tiropita, spanakopita or kotopita costs $14.50. (Sample these delicacies at St. George's annual festival May 3, 4 and 5.)

Acropolis Food Market, which has been in the Summar family since 1948, sells frozen spinach- and-cheese pies and baklava. A sheet of 48 spinach-and-cheese pies or baklava costs $18.75; 41/2 pounds of imported stuffed grape leaves (more than 100 leaves) cost $9.50. Some of Washington's most famous caterers shop here. uf678>St. George Greek Orthodox Church, 7701 Bradley Blvd., Bethesda. 469-7990. Acropolis Food Market, 1206 Underwood St. NW. 829-1414. CHINESE

The largest selection of carryout frozen dim sum in Chinatown can be found at Da-Hua Foods. Brought in from New York's Chinatown, the dim sum range from shrimp sumai to egg rolls to sweet buns and cost upward from $1.25 a dozen. Your local Chinese restaurant will probably prepare dim sum to go, too.

Da-Hua Foods, 617 I St. NW. 842-1992. CONTINENTAL

For miniature quiches lorraine ($6 per dozen) or danish pastries and croissants (20 cents each) and tiny French pastries ($5.76 a dozen), visit Swiss Pastries Inc. Allow one day's advance notice for your order.

Swiss Pastries Inc., 2377 Lewis Ave., Rockville. 881-8158. Closed Mondays. JEWISH BAKED GOODS

For those who love the Russian coffeeca and German rye bread sold at Montgomery Farm Women's Market, try Deluxe Bake Shop in the White Oak shopping center. The rye bread, in 41/2- to 8-pound rounds, is $1.09 a pound; Russian coffeecake is $2.98 a pound. Deluxe also sells miniature cheese danish ($4.75 a dozen) and challahs ranging from roll size to 15-pound loaves.

Deluxe Bake Shop, 11255 New Hampshire Ave., Silver Spring. 593-6607. CHEESE

Rounds of brie and Stilton cheese are nice to have as insurance for guests who won't eat anything else. Both Potomac Butter and Egg Co. and Bethesda Co-op have great buys on cheese. The Co-op's 8-ounce miniwheel of Explorateur is $3.15 (larger wheels can be ordered 10 days in advance); a whole 5-to-6-pound wheel of brie is $3.29 a pound, and the price of pignoli nuts ($4.49 a pound) can't be beat in Washington.

Potomac Butter and Egg Co. Inc., 220 E St. SW. 554-9200. Bethesda Co-op, 7945 MacArthur Blvd., Bethesda. 320-2530. FISH

As the weather gets warmer, Washington becomes a fish- serving city. For your next crab feast try Bethesda Crab House, which will supply a bushel of steamed crabs, along with seasonings, vinegars, hammers, knives and bibs, for between $49 and $75 (price varies with the seasons, but is lower after July 4).

Or have an oyster bar complete with shucker. Moe Cherame of Old New Orleans Seafood Market will provide shuckers ($100 for the bar and the attendant plus 30 cents per Louisiana oyster). Gumbo, seafood chowder, bouillabaisse or jambalaya are $3.50 a pint.

For smoked salmon, caviar and,es, many of Washington's French chefs visit Gourmand in Arlington, which supplies sliced Norwegian salmon ($14.50 a pound) and Sevruga black caviar ($170 a pound).

No hors d'oeuvre is as "in" these days on the Washington cocktail party circuit as sushi. Most local restaurants help the caterers, so why not ask your corner sushi bar to help you? Fisherman's Marketing Co. in Glen Echo Shopping Center prepares 10 pieces of miniature sushi for $4.95 or 14 pieces of large sushi for $7.95. Allow three days' advance notice.

Crabs and shrimp: Bethesda Crab House, 4958 Bethesda Ave., Bethesda. 652- 3382. Oysters, gumbo, chowder, bouillabaisse and jambalaya: Old New Orleans Seafood Market, 6232 Old Dominion Dr., McLean. 237-7755. Salmon, caviar and,e: Gourmand, 2575-B Shirlington Rd., Arlington. 920-2941. Sushi: Fisherman's Marketing Co., 7307 MacArthur Blvd., Bethesda. 229-2526. ASPARAGUS, ENDIVES AND STRAWBERRIES

You may not be a favorite customer at a wholesale produce market -- unless you are buying 12 cases of endives or a dozen flats of strawberries -- but so what? They still will sell you just one case. Call early in the morning before you venture down to what seems to be the most reliable.

Isaac Kossow Inc., 1338 Fifth St. NE. 543-4340 (recorded phone orders only). Saturday orders must be placed by 7:30 a.m.