TWO YEARS AGO when she was 11, my daughter Elissa walked into the kitchen one afternoon and announced: "Hey, Mom, I've decided to become a vegetarian because I think it's mean to kill animals."

It was the kind of statement to which a parent has 10 seconds to make some kind of response. Several snappy rejoinders flashed through my mind:

"The heck you are!"

"Why isn't it mean to kill vegetables?"

"Then you can fix all your own food."

But somewhat to my own surprise, I actually ended up saying, "Okay, let's try it for awhile and see how things work out."

Two years later things are still working out, despite some definite readjustments in our life style. Elissa's a healthy teen-ager, even though she hasn't knowingly eaten a bit of animal flesh since the day she took her vow. Our family has discovered that a satifying dinner doesn't have to mean spaghetti with meat sauce. And I've learned how to make sure that a vegetarian diet is both tasty and nutritious.

Of course, it hasn't all been easy as pie. Before Elissa made her dramatic announcement, our family was eating a fairly typical American diet with a bit more emphasis on whole grains, fresh vegetables and low sugar snacks and desserts. So Elissa's younger brother Ethan was initially quite resistant to vegetarian meals. ("If we're not having meat for dinner tonight, I'm going to McDonalds.") And I found that changing long established cooking habits, like relying on ground beef for quick meals, was difficult.

But, on balance, making the effort has been worth it. As I've assured my husband many times, "Our diet is much helthier because we're eating less fat and more fiber. And besides, there are a lot worse ways a teen-ager can show her values are different from her parents' than by becoming a vegetarian."

Like any concerned mother, before I let my daughter turn her eating habits upside-down, I checked out her diet nutritionally. Besides vegetables she will eat dairy products, eggs and tuna fish, although I'm not sure why this latter is an honorary vegetable.

From reading several books and articles I found that the protein in dairy products is every bit as good as the protein in meat. And eggs are even better. What's more, I learned how to provide high quality protein by combining vegetable sources with each other and dairy products at the same meal. So instead of a meat entree these days, we might have a bean and rice casserole, a cream of vegetable soup, Mexican-style corn and beans, or a vegetable quiche.

Vitamins and minerals don't have to be a problem either. Although vitamin B12 is not found in vegetables, it is abundant in dairy products. The key to getting the other vitamins and minerals the body needs is in eating a wide variety of grains and vegetables. Legumes, nuts and seeds, for example, have B vitamins and iron. Grains are good sources of thiamin, iron and trace minerals. Dark green, leafy vegetables have calcium, riboflavin and carotene (a precursor of vitamin A).

Findings good recipes was my next concern. Two books that got me started were "Recipes for a Small Planet," by Ellen Buchman Ewald, and "Diet for a Small Planet," by Frances Moore Lappe. Both emphasize vegetable and/or dairy combinations that provide high quality protein. Other well thumbed volumes on my kitchen shelf include "The Moosewood Cookbook," by Mollie Katzen, and "Laurel's Kitchen," by Laurel Robertson, Carol Flinders and Bronwen Godfrey.

In general our whole family now sits down to a vegetarian dinner two to four times a week. For the first six months, Ethan made me recite the ingredients of each mysterious new dish before he'd put fork to mouth. But after awhile, even he developed some vegetarian favorites. Last week, for example, he actually requested Curried Lentil Soup.

Sometimes I do all the cooking. But often the kids help. Both can follow a recipe like veteran cooks. And Ethan likes to make his own statement with the spice bottles.

Some evenings we fix two meals -- one with a small amount of meat and the other strictly vegetarian. Often these are dishes like chili con carne and chili sans carne where the preparations are similar. The next night we might have two sets of leftovers. Or we may freeze individual servings of the vegetarian leftovers for Elissa to eat when the rest of us want meat.

Other evenings I cook a vegetarian dish -- such as lasagna -- to which a meat sauce can be added. In fact, this sort of compromise has become a standard company meal, since we don't like to keep our vegetarian in the closet. Desserts are fruit and sometimes whole grain baked goodies, although the males in the household still insist on stocking the freezer with ice cream. t

Breakfasts now emphasize fiber and protein. We might have an egg dish with whole grain toast, or cottage cheese-whole wheat pancakes. But some of our other standbys include open-faced toasted cheese sandwiches and peanut butter on whole wheat toast.

Both children buy lunch at school -- with Elissa opting for the salad bar which features cottage cheese, garbanzo beans, and chopped egg for protein.

Because I'm concerned about nutrition, I include lots of dry beans and peas, soy products, whole wheat pasta, natural grain bread, cheeses and whole grains such as brown rice, bulgur wheat and barley in our menus. And to keep costs down I've joined a natural food co-op.

Here are some of the recipes that my family now considers favorites: CREAMY POTATO-CARROT SOUP (4 servings) 8 medium potatoes, peeled and diced 1 large vegetarian boullion cube (sold at health food stores) or 2 regular vegetarian boullion packets sold at grocery stores 3 cups water 3 cups milk 1 teaspoon dry basil 3 medium carrots, peeled and sliced salt and pepper to taste 2 tablespoons butter

Combine potatoes, bouillon, water, milk and basil in a large, heavy pot. Cook over medium heat, stirring occasionally until potatoes are tender. Meanwhile, in a separate pot, cook carrots in boiling water until tender. When potatoes are done, use a portable mixer or potato masher to blend them into the cooking liquid. You can make the soup almost smooth or leave fairly large pieces of potato to add texture. When the carrots are cooked, drain off water and use the portable mixer or potato masher to break them up slightly. Add carrots to potato soup. Stir in butter. Season with salt and pepper to taste. Add additional basil if desired. GARBANZO BEANS AND BROWN RICE IN PITA (3 or 4 servings) 1 clove garlic, minced 1 medium onion 3/4 cup green pepper, chopped 1 to 2 tablespoons cooking oil 1 can (15 ounces) garbanzo beans, drained 1/2 cup water 2 1/2 cups cooked brown rice 1/2 teaspoon marjoram 1/4 teaspoon turmeric 1 drop hot pepper sauce 1/4 teaspoon thyme 1/2 teaspoon salt 4 large pita breads cut in half lettuce and tomato for garnish

In a medium saucepan, saute garlic, onion and pepper in oil until onion is very limp. Reduce heat and add garbanzo beans and water. Stir in rice. Add seasonings. Cover and cook over low heat about 20 minutes, stirring occasionally, until flavors are blended. To serve, spoon mixture into pita bread pockets. Garnish with lettuce and tomato. NOODLE OMELET (8 servings) 2 tablespoons butter 1 tablespoon oil 1 cup chopped onions 2/3 cup green pepper, sliced into 1-inch strips 1 cup grated cheese (smoked cheddar is delicious) 8 eggs, beaten 2 1/4 cups whole wheat noodles, cooked 1 teaspoon salt

Melt 1 tablespoon of the butter and oil together in a 10-to-12-inch frying pan. Saute onion and green pepper until the onion begins to brown. Stir in the second tablespoon of butter and keep the pan warm over very low heat.

Stir together the cheese, eggs, cooked noodles and salt. Pour the mixture over the sauteed vegetables, cover, and cook without stirring over medium-low heat for 15 to 20 minutes. You may sprinkle extra grated cheese over the top during the last few minutes of cookng. When done the casserole will be slightly puffed, browned around the edges, and firm to the touch. Serve.