Maida Heatter, who brought us "Great Desserts," "Great Cookies," "Great Chocolate Desserts" and is now tempting us with "Great American Desserts" (Knopf, $25), will be presiding at a dessert tasting and book signing at Williams-Sonoma (Mazza Gallerie) tomorrow at 1 p.m. What are some great American desserts? If the grande dame of sweets' samplings tomorrow are any indication, they include not only chocolate cake and brownies, but sweet potato pound cake and tomato soup cake as well. Sweet Blasts From the Past

American confections will also highlight Alexandria's Carlyle House bake sale and craft exhibition Saturday, but the fare will be strictly 18th century. From 10 a.m. to 4 p.m., king cakes, bath cakes and other baked goods will be on sale as part of the estate's Merchant Day celebration; procedes will go toward purchasing furnishings for the historic Georgian mansion built in 1752, located at 121 North Fairfax St. Here's a taste from the past, a recipe for ginger cookies to be served at the Carlyle House this weekend. GINGER-BREAD (Makes about 30 cookies)

2 cups flour

1 teaspoon salt

1 cup sugar

1 tablespoon ginger

2 teaspoons dried lemon peel

1 cup (2 sticks) butter

1 tablespoon each citron and candied orange peel, chopped (optional)

1/2 cup molasses, approximately

Combine the flour, salt, sugar, ginger and lemon peel. Add butter, working it in with finger tips or pastry blender, followed by optional citron and orange peel. Add only enough molasses to hold the ingredients together. Chill the mixture 2 hours. Form into 1-inch balls and flatten slightly (or roll dough out very thin, then cut into 1 1/2-inch rounds). Place on buttered baking sheets and bake in a 350-degree oven approximately 7 to 9 minutes. From "Antique Desserts," by Hope Peck (Constantia Books, 1977). Lobster-Lovers Take Heed

Unlike other commemorative occasions, Lobster Day falls twice a year -- once in summer, and once in autumn when Ed Rindler of Finestkind Lobster arrives from Maine with a truckload of delectable fresh crustaceans. This year, the pickup date falls on Oct. 19, and Rindler notes that "the fall product is even sweeter than June's, as it has just completed its shedding cycle and grown new meat and shells."

The price is $7.50 a pound for orders placed by Oct. 5 (with a five-pound minimum) and $8 a pound thereafter. Each five-pound order consists of four live lobsters, weighing an average of 1 1/4 pounds each. To order, call (202) 543-0311, give your name and address, and Rindler will send an informational kit.

Also available are steamer clams, which come pre-washed and pre-packed in seaweed. The cost is $30 per peck (about 200 steamers, or enough to serve six to eight).

The pickup sites include: the U.S. Capitol parking lot, 8:30-11:30 a.m.; National Institutes of Health (parking lot 31G) in Bethesda, 1:30-3:30 p.m.; Melpar E-Systems, 7700 Arlington Blvd. (Route 50) in Falls Church, 8:30-11:30 a.m.