A CUSTOM-MADE, dinner-size sandwich with a burger and all the trimmings has always been a favorite American standby.But who says the burger has to be made out of ground beef?Lots of other flavorful and nutritious burgers can be prepared from a variety of beans and grains. Some are remarkably reminiscent of traditional hamburgers; others provide a great change of taste in a familiar setting.

The following is an interesting selection of high-protein, vegetarian burgers that are easy to make as well as being easy on the budget. The recipes have been chosen because of their broad taste appeal -- even for those who haven't sworn off meat.

The covnient size of these burgers (compared to vegetarian loaves) makes them a cinch to wrap for the freezer, and a breeze to quickly warm up in a toaster oven or microwave oven, if either is available. Of course, they can also be kept in the refrigerator for two or three days, and are even tasty eaten cold.

In general, however, these burgers taste best served warm inside a pocket of whole-wheat pita bread or with English muffins or hamburger buns. Garnish them with your choice of lettuce (or other greens), tomato slices, alfalfa sprouts, bean sprouts, thin cucumber slices and/or yogurt. LENTIL-RICE BURGERS (Makes about 12 burgers)

These look and taste more like meaty hamburgers than the ingredients from which they are made. 1 cup dry lentils 1/2 cup raw brown rice 3 cups water 1 large egg, lightly beaten 1 cup fresh whole-wheat bread crumbs (use approximately 2 slices) 1/2 cup wheat germ 1 medium onion, grated or finely chopped 1/2 teaspoon celery seed 1/4 to 1/2 teaspoon cumin seed (to taste) 1/2 teaspoon marjoram 1/2 teaspoon salt 1/4 teaspoon freshly ground pepper 1 egg beaten with 1 teaspoon milk Extra wheat germ, bread crumbs or bran

Wash lentils. Place in medium saucepan with raw rice and 3 cups water. Bring to boil, then lower heat and simmer about 45 minutes or until lentils and rice are tender. Remove from heat. Let rest about 10 minutes, then mash lightly with any water remaining in pan. (This may be done in advance.)

Add next nine ingredients (up to and including pepper), and mix well. Use about 1/3 cup of the mixture for each burger patty. Coat each burger with beaten egg and milk, then with extra wheat germ, bread crumbs or bran. Place on a greased cookie sheet or jelly-roll pan. Bake in a preheated 400-degree oven for about 20 minutes, or until outside is crunchy, and inside is cooked through.

(Alternatively, you may omit the egg coating and simply coat the lentil burgers with some wheat germ. Then fry them in a small amount of oil until they are lightly browned on both sides.) MILLET BURGERS (Make about 15 burgers) 1 tablespoon oil 1 cup raw millet 1/8 teaspoon cayenne 2 3/4 cups boiling water 1 teaspoon salt 1 medium onion, grated or finely minced 2 medium carrots, grated 1/4 cup wheat germ 1/4 cup bran 1/2 cup soy flour 1 cup fresh whole-wheat bread crumbs (use approximately 2 slices) 2 large eggs, lightly beaten 1/2 cup finely minced fresh parsley 1/2 teaspoon thyme

Heat oil in a large saucepan. Add millet and cayenne, and stir until all grains are coated with oil. Continue to stir, over medium heat, another 2 minutes. Add boiling water and salt, reduce heat and simmer about 35 to 40 minutes, covered. About 5 or 10 minutes before millet is done cooking, add onion and carrots and mix in. Remove cooked millet from heat when it is done and all the water is absorbed.

Add remaining ingredients and mix well until everything is completely combined. Let mixture rest a few minutes until it is cool enough to handle. Using about 1/4 cup for each, shape mixture into burgers. Fry with a small amount of oil in a skillet set over medium heat, until lightly browned on both sides (about 10 minutes all together). HERBED SOYBEAN BURGERS (Makes 6 to 8 large burgers) 1 (16-ounce) can soybeans, drained 1/2 medium onion, finely chopped 1/8 teaspoon garlic powder 1/2 cup instant nonfat dry milk mixed with 1/4 cup water 1/4 to 1/2 teaspoon rosemary (to taste) 1/2 teaspoon thyme 1/2 cup finely chopped fresh parsley 3 tablespoons wheat germ 1 large egg, lightly beaten 1/2 teaspoon salt 1/8 teaspoon freshly ground pepper Fresh whole-wheat bread crumbs

Mash soybeans using a food processor, food mill or meat grinder. They should be reduced to very small chunks, not turned into a paste. Then combine beans with remaining ingredients except bread crumbs. Shap mixture into burgers. Coat each burger with bread crumbs. Arrange in a shallow, oiled baking dish, and bake at 375 degrees for 20 to 30 minutes, or until golden brown. TOFU-BULGUR BURGERS (Makes about 16 burgers) 2 cups water 1 teaspoon salt 1 cup bulgur (or cracked wheat) 1 pound drained, hard or soft tofu (bean curd), 2 large eggs, lightly beaten 1/2 cup fresh whole-wheat bread crumbs (use approximately one slice) 1 medium onion, grated or finely minced 1 1/2 teaspoon basil 1 teaspoon oregano 1/2 teaspoon thyme 1/2 teaspoon garlic powder 1/4 teaspoon freshly ground pepper 1/4 cup grated Parmesan cheese 1 cup whole-wheat (pastry) flour (or a little more)

Put water and salt in a medium saucepan, and bring to a boil. Add bulgur, lower heat and simmer, covered, for 10 to 15 minutes, or until all water is absorbed. (You may leave the cover off for the last few minutes to speed up the process.)

Meanwhile, use your fingers or a fork to mash the tofu (bean curd) in a large bowl. Beat in the eggs, then add the remaining ingredients. When the bulghur is done cooking, add it as well, then mix everything until well combined. The mixture should be sticky, but firm enough to form into burgers. If it is too soft, add a little more flour (amount will depend on the brand of tofu and how wet it is).

Using about 1/4 cup for each, shape the mixture into burgers that are about three inches in diameter. Fry in a small amount of oil in a skillet set over medium-high heat, until lightly browned on both sides (a total of about 8 minutes). Drain on paper towels, if desired. TOFU-BULGUR BURGERS PARMIGIANA (4 to 6 servings)

Overlap cooked Tofu-Bulgur Burgers in a greased 8-x-12-inch or 9-x13-inch baking dish. Pour over tomato sauce to cover, and sprinkle with oregano, basil, salt and pepper to taste. (Or use spaghetti or pizza sauce.) Cover top with coarsely grated or thinly sliced mozzarella cheese. Bake in a 350-degree oven about 15 minutes, or until cheese is melted and bubbly. Note: Amounts of ingredients are not critical; use as much as you desire.