Reeling from slow milk sales and bad publicity about surplus stores of cheese, butter and nonfat dry milk, dairy farmers are attempting to improve their image.

For the first time, June Dairy Month will have a national kick-off day--a public relations extravaganza sponsored by the U.S. Department of Agriculture and the Mid-Atlantic Milk Marketing Area. Come Saturday, three acres of festivities parked on the lawn in front of the USDA will offer visitors insight into dairy farming and products.

Activities, scheduled to begin at 10 a.m., will include cooking demonstrations by representatives from the Baltimore Culinary Institute who will make, among other things, ice cream, yogurt and cheese.

A portable dairy farm exhibit, contained in two tractor trailers, will include four cows, and a miniature barn, feed room, milking parlor and milk room.

Those who are bullish on world records should hang around when they unload what is alleged to be the world's largest cheese sandwich at 12:30 p.m., just in time for lunch. Many other family activities are scheduled.

The roundup will include a cow-milking contest, a milk-drinking contest, a calf-petting zoo, displays of antique and contemporary farm equipment and a life-sized cow carved from real butter.

As of April 9, the USDA owned 365 million pounds of butter, 625 million pounds of cheese and 975 million pounds of nonfat dry milk. Uncle Sam buys these products to keep dairy prices up so the farmers can afford to keep their farms and cows.

Dairy Month promotion may cause an imperceptible dent in the swiftly increasing stocks of milk products. But these products remain the best and most easily accessible sources of calcium in our diets. In addition, they contribute high-quality protein, B vitamins and vitamin A. Milk, yogurt and cheese provide the base for protein-packed meatless main dishes and sturdy, refreshing summer breakfasts. Since eating dairy products may come to signify patriotism, two Express Lane menus are provided here, one breakfast, one dinner.

Every kitchen should be equipped with flour, sugar, salt, pepper and butter or oil (for Dairy Days, butter of course).

EXPRESS LANE LIST (Breakfast): Yogurt, peach or apricot nectar, banana.

EXPRESS LANE LIST (Dinner): Milk, cheese, eggs, red pepper, bread crumbs or bread for crumbs, tomatoes, garlic, basil.

PEACH VELVET (2 to 3 servings) 12 ounces peach or apricot nectar 1 cup plain yogurt 1 banana 4 ice cubes

Combine ingredients in a blender at high speed until smooth. Pour into glasses.

CHEESE CROQUETTES (3 to 4 servings) 3 tablespoons butter 1/4 cup flour 2/3 cup milk 1 1/2 cups grated cheese (combine two hard cooking cheeses such as old cheddar, swiss, gruyere or parmesan) 2 egg yolks, beaten 1 whole egg, beaten Salt and pepper Ground red pepper Bread crumbs

Melt butter in large skillet. Add flour and stir about 1 minute over medium heat. Add milk, whisking constantly, so mixture thickens without lumps. Add cheese and stir until it melts. Remove from heat, whisk a little of the mixture into beaten egg yolks and whisk this back into cheese mixture. Season with salt and peppers and set aside to cool. (Begin preparing tomatoes). When cool and firm, shape portions into cylinders (or cut the mixture into squares or rectangles). Dip croquettes into beaten egg and then in bread crumbs. Saute' in butter or deep-fat fry in hot fat (375 degrees) until golden. Serve with stewed tomatoes.

ITALIAN STEWED TOMATOES (4 servings) 8 to 12 ripe tomatoes (preferably plum tomatoes) or 2 pounds canned tomatoes 2 tablespoons butter 1 to 2 cloves garlic, minced 1 teaspoon basil Salt and pepper to taste

Peel tomatoes by dropping them briefly into boiling water, or drain canned tomatoes well. Melt butter in a large skillet and add garlic. Stir about 1 minute and add tomatoes and basil. Stir to break up tomatoes somewhat and heat them through. Salt and pepper to taste