WHEN a three-year drought left cattle farmers Robert and Elizabeth Schwartz high and dry in 1977, the Rhoadesville, Va., couple switched from raising beef to strawberries and other fruits and vegetables.

Today, the Schwartzes' pick-your-own farm is such a success that there are only a few head of cattle left, "just to keep the grass down."

The advantages of raising strawberries over cows are not all economic. For one thing, strawberries smell better. Country air takes on new meaning when your house boarders a 13-acre field of blooming strawberries, says Elizabeth Schwartz.

It's strawberry season, and you can pick the fruits of the Schwartzes' labors at their Double B Farms--one of more than 100 PYO farms in the Washington area. Over the next three weeks, the peak of the picking season, city dwellers can take advantage of the opportunity to take a drive into the country and buy vine-ripened strawberries at reduced prices. For the farmer, it's an opportunity to sell his goods directly to the consumer, eliminating the middleman and some of the overhead.

"Be sure to dress comfortably," Elizabeth Schwartz advises her customers, since the average picker spends at least an hour gathering about nine pounds of berries. "I tell them to eat as many as they want. The only rule is to leave the plants in the ground."

Pick only small to medium, plump strawberries with full red color, firm flesh, natural shine and fresh-looking green tops, says Anne Prince, a home economist with the Fairfax Department of Extension and Continuing Education. Avoid strawberries with white tops, since they do not ripen appreciably after being picked. Prince recommends calling PYO farms ahead for hours and prices, and to find out if pails or trays for gathering are supplied and whether children are allowed.

Pinch the berries off the plant between your thumb and forefinger. Pulling them loose from the stem can bruise the berry, loosen the cap (causing a loss in moisture) or damage the plant. Store them loosely in small containers.

Once the berries are picked, store them in the coolest location in your car. The summer heat of a car trunk will turn the firmest berries into mush by the time you get them home, Prince warns. Store the berries in the refrigerator and eat or preserve them within a day or two.

To prepare strawberries, wash them in lukewarm water just before using, only then removing the green caps. Separate the berries according to their firmness. The softer berries should be used in jams, pure'es or a bread recipe such as the one that follows. Use firm berries for Schwartz's strawberry appetizers--fat berries wrapped in a thin slice of prosciutto, dipped in sour cream and yogurt and sprinkled with pistachio nuts. Peppered strawberries are a authoratative dessert, peppery and alcoholic, and contrast beautifully with papaya or mango slices.

Strawberries can be frozen with or without sugar. For unsweetened berries, wash, drain and pat dry. Remove the stem and pure'e or leave whole. Place whole strawberries in a single layer on a cookie sheet, pure'e in freezer cartons, leaving 1/2-inch head room for expansion. If you want to sweeten the berries before freezing add 3/4 cup of sugar to every four cups of prepared berries. Stir over low heat just until sugar dissolves. Pack into freezer containers leaving 1/2-inch of head space and freeze.

See Friday's Weekend section for a listing of pick-your-own farms. ELIZABETH SCHWARTZ'S STRAWBERRY BREAD (Makes 2 loaves) 3 eggs 1 1/2 cups sugar 1 cup salad oil 1 tablespoon vanilla 2 cups flour 1 cup quick oats 1 tablespoon cinnamon 1 teaspoon baking soda 1 teaspoon salt 1/2 teaspoon baking powder 2 cups crushed strawberries

Beat eggs and sugar; add oil and vanilla. Mix in flour, oats, cinnamon, soda, salt and baking powder. Add strawberries and mix well. Pour into two greased and floured 4-by-8-inch loaf pans. Bake 1 hour at 350 degrees. STRAWBERRY APPETIZERS (Makes 2 dozen) 3 ounces thinly sliced prosciutto, cut into 3-by- 3/4-inch strips (substitute country ham) 24 large strawberries 1/4 cup sour cream 1/4 cup plain yogurt 1/2 teaspoon grated lemon peel 1/4 cup finely chopped pistachios

Wash strawberries and hull. Wrap 1 strip prosciutto around each strawberry. Combine sour cream, yogurt and lemon peel in small bowl. Dip hull end of each strawberry into cream mixture, then into pistachios. Arrange coated berries, pistachio ends up, on serving plate. PEPPERED STRAWBERRIES (From Charley's Crab) (4 servings) 1 pound strawberries, stems removed and left whole (about 1 1/2 pints) 1 teaspoon coarsely ground pepper 4 tablespoons sugar 1 tablespoon pernod 1 tablespoon Grand Marnier 4 tablespoons heavy cream 2 papayas (substitute mangoes)

Wash strawberries, pat dry and hull. Sprinkle strawberries with pepper. Add sugar and toss gently. Add pernod and Grand Marnier and toss gently. Add cream and toss gently. Peel papayas, halve and scoop out seeds. Cut down through center and fan out and top with strawberry mixture.