AS WITH most grassroots movements, the salad greening of America has finally reached Capitol Hill. Last year the Senate cafeteria introduced a salad bar featuring fresh ingredients, among them several items not mentioned in the platform of either major party and generally considered to be the property of the natural foods constituency.

The spring MotherHerb, as the natural foods salad bar is known, was transplanted outdoors and until the recent heatwave it was thriving in the courtyard of the Russell Office Building. Jay Treadwell, director of food service for the Senate, promises that MotherHerby will weather the heat. He explained that staff members select prepared fruit or vegetable salads from the cart, or make their own. In addition freshly made breads and natural fruit drinks are sold.

The salad bar itself consists of the fruit plates and two salad mixtures, spinach plus (spinach, cherry tomatoes, mushrooms and chips or American and Swiss cheese) and lettuce (bibb, romaine, Boston and red cabbage). Condiments include apple sauce, a mixture of tomatoes and peppers in a basil, mustard and oil marinade, marinated squash, a tapanade (a tuna fish spread), home ground peanut butter and at least four breads prepared in the Senate bake shop.

Attendents in Yellow MotherHerb T-shirts work under the direction of Dee Williams. The diners eat on benches or, in picnic style, on the grass. Here are recipes for some of the offerings the consume. POTATO SALAD (8 servings) 6 medium to large potatoes 3 hard cooked eggs 3/4 cup chopped onions 3/4 cup chopped celery

Peel and boil potatoes for 20 minutes. Dice and cool. Chop eggs, onions and celery. Add to potatoes and add special dressing mix until well blended. Do not crush potatoes. Dressing Mix 1/2 cup plain yogurt 1/2 cup milk 1 teaspoon honey 1 teaspoon lemon juice Mix ingredients together COTTAGE CHEESE SPREAD (6 servings) 3 cups cottage cheese 4 ounces ricotta cheese 1/2 teaspoon drill seeds 1/2 teaspoon sunflower seeds 1/4 cup carrots 1/4 cup radishes 2 tablespoons green peppers 2 tablespoons celery

Chop carrots, radishes, peppers and celery until fine. Add to mixture of cottage and ricotta cheese; grind dill seeds and sunflower seeds until fine; sprinkle into mix, stir until well blended. MOTHERHERBS' MAYONNAISE MIX 5 eggs 1 quart soy bean vegetable oil 2 tablespoons lemon juice 1/2 tablespoon paprika 1/2 tablespoon cayenne pepper

Put eggs in large mixing bowl. Mix on high speed for 4 to 5 minutes. Slow blender to medium and very slowly trickle in soy bean oil. After all oil has been added mix for another 10 minutes.Set mixer on slow speed and add lemon juice. Mix for another minute. Add paprika and cayenne pepper and mix for 15 seconds. CUCUMBER AND LEMON 3 cucumbers 1/4 cup lemon juice 2 tablespoons honey 3 tablespoons soy bean oil 2 tablespoons tamari soy sauce 2 tablespoons dill weed 3/4 cup sunflower seeds

Peel and thinly slice cucumbers, mix lemon juice, honey, soy bean oil and tamari sauce until well blended, add ground dill weed and sunflower seeds to mix, pour over cucumber and stir. Let stand 2 to 4 hours before serving. SAGE-MINT DRESSING (make 1 pint) 1 pint mayonnaise mix 1/4 cup parsley 1/4 teaspoon rolled or mashed anise seeds 1 1/2 teaspoon sage 1/4 cup mint

Chop parsley and mint until fine, add to mayonnaise mix. Sprinkle anise and sage into mix, stir until well blended. ROSEMARY, BASIL AND ONION DRESSING (make 1 pint) 1 pint mayonnaise mix 1/4 teaspoon mashed anise seeds 1/3 stalk spring onion, minced 3 cloves fresh garlic, crushed 3 tablespoon mashed basil 3 tablespoon rosemary

Chop onions and rosemary until fine; add garlic and onion to mayonnaise mix.

Sprinkle anise seed, basil and rosemary leaves into mix, stir until well blended.