THERE'S A persistent kitchen bacteria that has been the despair of good cooks for generations.

Discovered by ancient Egyptians, then rediscovered somewhere in the Midwestern United States during the early 18th century, these pesky little organisms traveled westward (in wagon trains, actually) and eventually reached San Francisco. This is not disease-carrying bacteria, but the microbes responsible for imparting the tangy flavor called sourdough to breads, pancakes and biscuits.

The trouble was -- although some amateur enthusiasts made a hobby of turning out fine sourdough products from ancient starters -- most people had to struggle for years to get a proper brew going. And then the yeast in the starter was apt to die out mysteriously for no good reason at all.

The myths and legends on how to keep a starter going were so numerous they could have filled a book.

It wasn't until 1972 that George K. York, a food technologist with the Department of Agriculture at the University of California at Davis, completed an analysis of sourdough starters that identified the particular strain of acidophilus bacteria that create the special characteristics of sourdough products.

It was not yeast, but a harmless bacteria found in raw milk, an organism also present in aged cheddar cheese, cultured buttermilk and yogurt. And he was able to develop a routine way to prepare sourdough starter from yogurt that does not rely (as much) on chance.

Since that time homemade sourdough bread has experienced a revival among Californians. In fact, Dr. York, who frequently gives demonstrations on how to bake bread, reports that the recipe has migrated eastward this time.

In a commercial bakery a piece of bread dough from one day's batch is allowed to stand at room temperature overnight to sour. This leftover dough is used to make a sponge-like batter which is also often soured before a final mixing, kneading and shaping. The whole process can take up to 48 hours.

In these recipes, provided by Dr. York, the sponge is soured by using the starter, thus shortening the time.

Before starting the bread, you will need to locate a warm place to put the culture, the starter and the dough. Suggested places include a burner near (but not on) the pilot light of a gas range, the top of a hot water heater or of a built-in refrigerator. An electric oven can be warmed slightly by turning it on the lowest setting until the air inside feels slightly warmer than room temperature. Keep it warm by turning on the oven light or propping the door open enough to keep the light on. Place the mixture in front of (but not touching) the light and about 2 to 2 1/2-inches below it. STARTER (Yields 1 1/2 cups)

Heat 1 cup milk to 90 to 100 degrees and put it in a clean, warm pint or quart jar. Add 2 tablespoons plain yogurt. (Non-fat milk and low-fat yogurt give the tangiest flavor.) Cover the jar tightly and allow starter to stand in a warm place for 18 to 24 hours. Temperatures of 80 to 100 degrees are ideal.

If a clear liquid rises to the top of the milk during this time, stir it back into the mixture. If the liquid has a light pink color, it indicates that the milk is breaking down. Discard it and start again.

After 18 to 24 hours, the starter will be the consistency of yogurt, a curd that doesn't flow easily when the container is tilted. After this curd is formed, gradually stir in 1 cup all-purpose or unbleached flour until the mixture is smooth. Cover tightly and let stand in a warm place (80 to 100 degrees) until the mixture is full of bubbles and has a good, sour smell. This will take from 2 to 5 days. The starter is now ready to use.

To keep the starter going you must feed it. Each time you use 1 cup of starter, replenish it with 1 cup warm milk. Use the same type of milk each time for consistent flavor.

When you are ready let it stand in a warm place over night or until it is bubbly. Then return it to the refrigerator to store. When you use it again, allow the starter to warm up to room temperature than add 1 cup flour to the starter and let it stand several hours before making the sponge.

If you bake regularly, the starter will remain alive and active. If you don't discard half the starter and replenish it every two weeks. Freshly-fed starter may be frozen for 1 1/2 to 2 months. When stored this way, you must allow it to thaw and to stand in a warm place for 24 hours or until it is bubbly before using it. SOURDOUGH FRENCH BREAD (Yields 2 loaves)

The sponge is made by combining 2 cups warm water, 1 cup starter, 1/4 teaspoons active dry yeast and 4 cups flour. Place the sponge in a bowl and cover with plastic wrap or a clean dish towel and allow it to stand in a warm place (85 degrees) for 6 to 8 hours or overnight. The sponge will be very thick and full of bubbles.

The dough will take about 6 hours. Add 2 teaspoons salt, 2 teaspoons sugar and 3 cups flour to the sponge. Turn the dough out onto a floured board and knead it until it is smooth and elastic (10 to 15 minutes). Add flour as needed to prevent the dough from sticking.

Place in a greased bowl and turn dough over once to grease top and sides. Cover the bowl and let the dough rise in a warm place until it has doubled in bulk, about 1 1/2 to 2 hours.

Punch dough down and divide it in half; shape into loaves. If you only have one oven, wrap one loaf in plastic wrap and refrigerate at this time.

Place the remaining loaf on a piece of cardboard sprinkled with cornmeal. Cover the loaf with plastic wrap or clean towel and let the loaf rise a second time for 1 1/2 to 2 hours. Make deep slashes at a slant for long loaves or crisscross slashes for round loaves using a sharp knife or a razor blade.

Bring 1 teaspoon cornstarch and 1/2 cup water to a boil. Cool slightly and brush the top and sides of the loaf with this.

Place the oven racks on the second lowest positions. Place a pan with 1/4-inch of water in it on the bottom shelf. Preheat oven to 400 degrees. Slide the bread onto a baking sheet and place it in the heated oven. After baking for 10 minutes, brush the bread again with the cornstarch and water solution. Continue to bake for 20 to 25 minutes more or until the loaf is golden brown. Cool on a wire-rack.

When you remove the second loaf from the refrigerator, remember that it will take longer to rise than the unrefrigerated loaf. When it has risen completely, place it in the oven and bake as directed. SOURDOUGH BISCUITS (Makes 20) 1 cup unsifted all-purpose flour 1 tablespoon baking powder 1/2 teaspoon salt 1/4 teaspoon baking soda 3 tablespoons granulated sugar 1/3 cup solid all-purpose vegetable shortening 1 cup sourdough starter Melted butter or margarine

Mix dry ingredients together. Cut in shortening until mixture resembled coarse crumbs. Stir in 1 cup starter until mixture is throughly moistened. It will be very sticky and wet.

Turn out onto a foured board and turn to coat with flour for easier handling. Knead lightly 20 to 25 times, adding flour sparingly.

A moist dough makes better biscuits. Roll out about 1/2 inch thick. Turn in melted butter or margarine.

Place on a baking sheet and let rise about 45 minutes. If there is a rush, however, this can be omitted. Bake 10 minutes at 400 degrees or until well-browned. SOURDOUGH RYE BREAD (Makes 2 loaves) 1 cup starter 2 cups rye flour 1 1/4 cups warm water 1 package active dry yeast 2 teaspoons salt 1 tablespoon caraway seeds 1 1/2 teaspoons poppy seeds 2 tablespoons melted butter or margarine 3 tablespoons granulated sugar 3 3/4 cups unsifted all-purpose flour Cornmeal 1 egg, slightly beaten with 1 tablespoon water

The day before preparing the dough, combine starter with rye flour and 1 cup warm water in a bowl. Cover with plastic wrap and let stand at room temperature overnight. The next day stir down the dough and add yeast dissolved in 1/4 cup warm water, salt, caraway, poppy, butter and sugar. Then add up to 3 3/4 cups unsifted all-purpose flour, 1 cup at a time, to make a stiff but workable dough. Knead for 10 to 12 minutes, then shape into a ball. Place in a buttered bowl, turning to coat the dough with the butter. Cover and let rise in a warm draft-free place until doubled in bulk, about 2 hours.

Punch down and divide the dough in half. Shape into 2 round loaves and place on a buttered baking sheet generously sprinkled with cornmeal. Cover and let rise again until doubled in bulk, about 1 hour.

Brush with egg wash, and bake in a preheated, 375-degree oven for 30 minutes or until lightly browned and the loaves sound hollow when tapped with knuckles. Cool, covering with towels to prevent the crust from hardening. SOURDOUGH PANCAKES (Makes 20) 3 cups starter 1/4 cup powdered milk, unreconstituted 2 tablespoons melted butter or margarine 1 large egg 2 tablespoons sugar 1 teaspoon salt 1 teaspoon baking soda

Mix starter, dry milk, butter and egg thoroughly. In a cup or small bowl, mix separately the sugar, salt and soda. Sprinkle sugar-salt-soda mixture on the batter and fold in gently but thoroughly. Let sit for a few minutes while griddle heats. Without stirring, spoon batter onto a very hot, greased griddle to make 2-inch pancakes. Do not overcook. When bubbles form on one side, turn over, continue to cook briefly on the second side. SOURDOUGH ORANGE MUFFINS (Makes 12) 1/2 cup dark brown sugar, packed 1 1/2 cups unsifted all-purpose flour 1/2 cup whole wheat flour 1 teaspoon salt 1 teaspoon baking soda 2 teaspoons grated orange peel 1 beaten egg 1/2 cup vegetable oil 3/4 cup sourdough starter 1/2 cup buttermilk

Heat oven to 375 degrees. Grease a 12-cup muffin tin. In a bowl, mix all dry ingredients throughly, breaking up any lumps of brown sugar. In a separate bowl combine egg, oil, starter and buttermilk. Pour all at once into a well in the center of the dry ingredients, stirring just enough to moisten and blend. Do not overmix. Batter will look lumpy.

Divide batter among muffin cups, bake at 375 degrees for 30 to 35 minutes or until firm on top and a toothpick inserted in the center comes out clean. Serve immediately with sweet butter and honey.