ASK TODAY'S cook to explain the difference between a fryer and a roaster and you are likely to get a blank stare in return. But the answer has become important now that chicken producers are promoting the sales of roasters, which cost considerably more than fryers.

Time was when the variety of chicken you bought was determined by how you were going to cook it. For a really tender chicken you might buy a capon (which was the last time you saw one of those in the market?). A roaster was the next in order. Very small, very young, tender chickens were called squads. Other chicken varieties were not suitable for roasting frying or broiling -- they were too old and too tough: Stewing chickens went into stews and fricassees; "over the hill" hens and roasters were good for nothing except soup, the meat diced or ground after it was cooked so it would be tender enough to chew.

All of that has changed. The miracle of modern poultry breeding has created the broiler-fryer (called fryer for short). It roasts, it fries, it broils, it stews, it fricasees, it poaches, it steams, it barbecues. In other words, the all-around chicken. At one time most fryers weighted 2 1/2 to 3 pounds. Now they can, and do, weigh up to almost five pounds.

While roasters are supposed to be larger than broiler-fryers, because they are older, that is not alwlays the case. Often chickkens labeled broiler-fryers weigh the same as the smaller roaster, though roasters weigh up to 7 pounds.

According to a poultry expert at the Department of Agriculture, "The difference between a fryer and a roaster is essentially a labeling deal." But the biggest difference for the shopper is the price: anywhere from 20 to 44 cents a pound difference, depending on where you shop in any given week and on whether or not you demand a specific brand of roaster, which will cost you at least 10 cents a pound more than a no-name roaster.

According to the president of the company that produces the most expensive roaster sold in Washington supermarkets, Perdue, "Roasters have more flavor than a regular chicken. They're good eating." Perdue sells 400,000 roasters a week and 3 million fryers.

And in the market where Perdue is the biggest name-brand seller, New York, it offers the public what it considers additional reasons for buying its roasters. Full-page ads in newspapers trumpet: "Now roast without risk."

Perdue suggests in its ad that people really don't how to roast a chicken, so the company will help them by providing a built-in thermometer, the kind you see on some varieties of turkey. The kind that often doesn't work. The ad says: "Most people are a little chicken to cook a big roaster. Because to cook one you have to rely on something very unreliable: your oven. You see, the temperature of your oven can vary as much as 75 degrees from what you set it for. So even if you time other roasters perfectly you still can't be sure they'll come out right."

Similar radio commercials are being aired in Washington.

If Perdue is correct, one wonders how these people with faulty ovens produce cakes and breads, even less forgiving about inaccurate ovens than chickens.

Whether or not you are afraid to roast a chicken, whether or not you care about the price difference, you may care about texture and flavor. So we conducted three blind taste tests. In one we compared a Perdue roaster with a Holly Farms fryer. In another we compared a no-name roaster with a no-name fryer. In the third test we compared the Perdue roaster with a no-name fryer and a no-name roaster. In one of the tests the Perdue roaster weighed two ounces more than the no-name roaster and no-name fryer. In another test the fryer weighed more than the Perdue roaster, and in the third test the roaster and fryer weighed the same. All of them were in the 3 3/4-to-5 pound range.

The chickens were roasted on a rack at 350 degrees. In one test they were stuffed; in two they were not. They were not seasoned and were basted twice with the pan juices only.

The similarity of the results was startling. All of the birds had too much fat, a frequent complaint among buyers of chickens for the last 10 years or so. fThe birds browned equally well. They were all done as expected after cooking them 15 minutes to the pound unstuffed and 20 minutes to the pound stuffed. On neither occasion did the thermometer in the Perdue roasters pop up, a signal that the bird is cooked, when the birds were done.

The consensus among those who tasted the birds, not knowing which was which, was that they were essentially the same, though one person preferred the fryer in the test comparing it to a Perdue roaster and a no-name roaster.

Is there then any other reason to buy a roaster instead of a fryer? Based on the fact that the bigger the bird, the more meat there is in relation to bone, a 6-or 7-pound roaster provides more meat than two 3-or 3 1/2-pound fryers. According to the USDA a fryer has 68 percent meat in relation to bone; a roaster has 77 percent. But that 9 percent difference is only worth it if the price difference between roasters and fryers is smaller than it is in the Washington area.

In terms of economics you are better off buying two 3-or 3 1/2-pound fryers in place of one 6-or 7-pound roaster when the latter cost 89 and 99 cents a pound and the former are on sale, which they are frequently, for 49 or 55 cents a pound. Even when the roasters are on sale at 79 cents a pound, the sale-priced fryer is still a better buy.

On the basis of edible weight, this is what you are paying: 99-cents-a-pound roasters cost you $1.29 a pound for edible meat; at 89 cents a pound the edible meat is $1.16 a pound; at 79 cents a pound the edible meat is $1.02; at 55 cents a pound the edible meat from a fryer is 81 cents a pound; at 49 cents a pound, the edible meat is 72 cents.

Broiler-fryer chickens are one of the few economical meats available these days. If you want to roast them, and don't trust your cooking instincts to tell you when one is done, and don't want to cut into the chicken, buy yourself a reusable thermometer that records temperatures instantly. When you think the chicken is roasted, insert the thermometer in the thickest part of the breast. Many experts say it should register 170 degrees. Even that figure, however, seems to be open to dispute. "Doneness" appears to vary with individuals. Perdue says its birds are ready when the thermometer registers 180 degrees. Julia Child says Americans like their chickens cooked to 190 degrees, but she prefers them cooked to to 175 to 180 degrees. Another cooking authority says 140 degrees.

If the experts can't agree, what is the novice to do? For first-time or previously unsuccessful roasters I make this heretical suggestion. Use a meat thermometer, and when it reaches 160 degrees, take the chicken from the oven and make a clean cut where the breast meets the drumstick. If the juices run clear yellow, the chicken is done. As a final check, tilt the chicken slightly so internal juices run out. If they are clear yellow, the chicken is considered done. After a few trials you will know what internal temperature agrees with your particular testes.

If you want to take advantage of fryers when they are on sale, and have freezer space, you might want to cook up a large quantity of them, make a stock and use the cooked chicken meat to produce a variety of chicken dishes that may be frozen for later use. CHICKEN STOCK (Makes 14 cups) 10 pounds chicken, cut up 10 cups water 5 carrots, scraped and halved 2 onions, quartered 5 ribs celery, cut in half 2 tablespoons salt 1 teaspoon peper

Combine ingredients in several pots, cover and bring to a boil. Reduce heat to simmer and cook for 30 to 40 minutes, until chicken is just tender. Strain stock. Set vegetables aside. Cool stock and remove fat. Freeze in portions suitable for family use or use in other recipes.

Either freeze chicken tightly wrapped in nonporous paper, such as two layers of heavy-duty aluminum foil, or use chicken in other dishes and freeze prepared dishes. Chicken pieces frozenwithout sauce or stock should not be frozen for more than 1 month.

Three pounds of chicken produces 2 304 to 3 1/4 cups white and dark meat.

The vegetables cooked with the chicken can be pureed in a blender a little at a time with some of the stock. You will need about 1/2 cup stock for vegetables used in the above recipe. The puree makes an excellent side vegetable dish when reheated slowly. EGG FOO YUNG (4 servings) 6 eggs, well beaten 1 cup bean sprouts 1/4 cup chopped onion 1/4 chopped mushrooms 1/2 to 1 cup scraps chicken meat 2 teaspoon soy sauce Salt to taste Sauce (recipe below)

Mix eggs, bean sprouts, onion, mushrooms, chicken meat, soy sauce and salt to taste. Heat about 1 tablespoon of oil in small skillet (about 4 or 5 inches) and add 1/4 of egg mixture to oil. Cook until eggs have browned on one size; turn and brown on other side. Repeat until all batter is used up. Keep pancakes warm while cooking the others. Serve with the following sauce.

Mix 1 tablespoon of cornstarch with 1 tablespoon cold water. Slowly stir in 1 tablespoon soy sauce and 1 cup chicken stock. Cook until mixture thickens. Serve hot over egg foo yung. CHICKEN IN SOY AND SHERRY (2 servings) 2 cups cooked chicken meat, cubed 1 egg white 1 tablespoon cornstarch 2 slices fresh ginger, minced 4 tablespoon oil 1/2 cup walnuts, toasted 1 tablespoon dry white wine 2 tablespoons soy sauce 1 teaspoon cornstarch mixed with 1 tablespoon water

Toast walnuts at 300 degrees for 10 to 15 minutes. Mix chicken meat with egg white, tablespoon cornstarch and ginger. Stir fry in hot oil in work or skillet for 1 minute, until chicken begins to take on color. Add wine and soy sauce. Cook 30 seconds more; then add cornstarch mixed with water and walnuts. Mix well and heat through. Serve at once with steamed rice. CHICKEN ON SPINACH BED (6 servings) 2 packages (10 ounces each) frozen spinach, cooked and throughly drained 4 tablespoons butter 1 clove garlic, mashed Dash each marjoram and basil 4 tablespoons flour 1/4 plus 3/4 cup heavy cream 5 cups cooked chicken meat, diced 3/4 cup chicken stock Salt and pepper to taste 1 cup freshly grated parmesan cheese (4 ounces)

Saute garlic, marjoram and basil in 1 tablespoon hot butter. Add and mix well 1 tablespoon flour. Stir in 1/3 cup cream and drained spinach. Place mixture in bottom of 2 1/2-quart casserole. Arrange chicken on spinach. melt 3 tablespoons butter. Remove from heat and blend in 3 tablespoons flour. Stir in 3/4 cup cream, chicken stock and cook until thickened. Season with salt and pepper. Pour sauce over chicken. Freeze if desired. To serve, defrost, cover with cheese and bake at 400 degrees for 20 minutes or until mixture is bubbly hot and cheese is melted. CURRIED CHICKEN WITH RAISINS (12 servings) 6 cups cooked diced chicken meat Flour Salt and pepper to taste 1/2 pound butter or margarine 1 1/2 teaspoons or more curry powder 6 medium tomatoes, cut up 3 green peppers, chopped 3 onions, chopped 1 small bunch parsley, chopped 1 stalk celery, chopped 1/2 pound currants or raisins 1/4 pound toasted, silvered almonds

Roll the diced chicken in flour that has been seasoned with salt and pepper.

Heat butter and stir in curry. Brown chicken in butter. Meanwhile, cook the tomatoes, peppers, onions, parsley and celery slowly, until vegetables give off juices and celery is tender but crisp. Combine chickens with vegetables and raisins. Heat through and serve sprinkled with almonds over steamed rice. Freeze if desired. CHICKEN AND RICE CASSEROLE (4 to 6 servings) 1 pound hot Italian sausage 1 1/2 cups chicken stock 1-by-3-inch strip orange peel 4 tablespoons salad oil 2 medium green peppers, seeded and cut in 1/2-by-1 1/2-inch strips 1 clove garlic, minced 1 1/2 pounds tomatoes, seeded and coarsley chopped Salt and freshly ground black pepper to taste 1 teaspoon oregano 1 2/3 cup raw rice, cooked 4 to 6 large pieces cooked chicken, skin and large bones removed 1 tablespoon finely chopped parsley

Place sausagaes in heavy skillet and cover with 1 cup chicken stock. Add orange peel and bring stock to boil. Prick sausages all over and cook 10 minutes. Drain and cool. Cut in 1/2-inch slices. Heat oil in heavy skillet and saute peppers until tender. Add garlic and cook another minute or two. Add tomatoes along with oregano, salt and pepper. Cook quickly for 5 minutes stirring. Remove from heat.

Arrange cooked rice in 3-or 4-quart casserole. Pour over 1/2 cup chicken stock. Place chicken pieces on top and then sausags. Top with tomato-pepper mixture. Freeze if desired. To serve, bake casserole at 350 degrees for 20 minutes, just to heat through completely. If ingredients are chilled, bake longer, 30 to 40 minutes. Sprinkle with parsley and serve. CHICKEN PAPRIKASH (4 servings) 4 tablespoons butter 1/2 cup finely chopped onion 1/2 pound mushrooms, sliced 1 tablespoon flour Pinch basil Pinch thyme 2 teaspoons imported Hungarian paprika, if available 2 tablespoons fresh dill or parsley, finely chopped 1/2 cup chicken stock and 1 cup dry white wine or 1 1/2 cups chicken stock Salt and freshly ground black pepper 3/4 cup sour cream or yogurt 2 teaspoon lemon juice 2 cups cooked chicken, diced

Cook the onions in hot butter until they color lightly. Stir in mushrooms and cook 3 minutes longer. Combine flour, paprika, basil, thyme and dill and them mix with onions and mushrooms. Off heat with wire whisk beat in the stock and wine. Return pan to heat and bring sauce to boil, stirring. Reduce heat and cook, stirring until it thickens. Reduce heat to barely simmering. Stir in sour cream or yogurt a little at a time. Do not allow sauce to boil or it will curdle. When sauce is hot fold and salt. Heat thoroughly but do not cook. Serve over noodles.