Americans have adopted certain Mexican dishes as their own, altering the ingredients and mode of preparation until they have become more American than Mexican. That is true of tacos made with fabricated shells rather than corn tortillas, tamales made with cornmeal rather than masa and most versions of chili.

To taste the "Mexican" food that many Americans grew up with one would have to find an old-fashioned soda fountain or diner where food is cooked to order. Unfortunately, these institutions have given way to fast-food franchises and impersonal commissary cooking. But the old recipes still exist. And a chance trip to a thrift shop yielded a book containing the traditional American versions of tamales and chili that appear here.

The book, "Soda Fountain and Luncheonette Management" by J.O. Dahl, was out of print for years before it was republished in 1945. The original date of publication is not given in this later edition.

"Soda Fountain and Luncheonette Management" was designed to help small-scale resaurant operators improve their business.

But Dahl also discusses menu planning and includes groups of recipes such s as "Seventy-two Profitable Sandwiches," "Fifty-Five Popular Toast Dishes," "Ninety-Eight Fountain Profit-Makers" and "Desserts That Ring the Register."

Fountains and luncheonettes, he sid, "are primarily for people who are in a hurry, who want to eat lightly, or who like a sweet or liquid diet, and for the multitude who want to eat at a low price." Therefore the food had to be economical as well as simply served.

Tamales and chili appear, along with "italian spaghetti" and "Chinese chop suey," in a chapter on "Profitable Salads and Specialty Dishes."

Chili a la Becker is a fresh and simple dish. One should prepare it in "a heavy bottomed sautoir or old-fashioned iron skillet," according to Dahl. The pan is first rubbed with a crushed clove of garlic. Then onion, green pepper, mushrooms and celery are cooked in butter. Instead of ground beef, pork is used. Beans, tomatoes and chili powder are added and the mixture is simmered for 30 to 45 minutes "to assure thorough blending of the various flavors, which is the only way to obtain good results."

Dahl attributes the recipe for Hot Tamales to Emory Hawcock, author of "Salads, Sandwiches and Specialty Dishes."

The tamales are not filled with pre-ground beef but with meat that has been cooked, then chopped and mixed with vinegar, chili powder and other seasonings. Shredded chicken also goes into the filling.

The cornmeal mush that coats the tamales is made with cornmeal, chili powder and broths from cooking beef and chicken.

The tamales can be wrapped in cornhusks or in parchment paper. "Personally I prefer the parchment, because it is uniform, attractive, sanitary and much easier to handle," wrote either Hawcock or Dahl (the "I" is not identified). However, in testin g the recipe, we found the cornhusks more satisfactory because the tamales do not stick to them as they do to parchment.

The recipe ends with these serving instructions: "Open the tamales but leave them on the shucks. Spread over a spoonful of tamale or barbecue sauce, or serve with thin rye bread and butter sandwiches and a side dish of Mexican slaw. Garnish with lettuce leaves and dill pickles or pimiento cheese balls."

Here are the recipes, slightly adapted from their original form. The tamale recipe has been cut in half, and readers might like to halve the quantity off vinegar given if they don't like strong vinegar taste in the filling. CHILI A LA BECKER (4 to 6 servings) 1 clove garlic, crushed 2 tablespoons butter or oil 1 medium onion, minced 1 large green pepper, minced 2 or 3 mushrooms, chopped 1/4 cup chopped celery, optional 1 pound minced pork, with fat 1 teaspoon chili powder 2 or 3 tomatoes, peeled and chopped 2 cups drained canned kidney beans 1/2 cup water Salt

Rub heavy skillet with crushed clove of garlic. Melt butter in skillet. Add onion and green pepper and cook for a few minutes but do not brown. Add mushrooms and celery and cook without browning. Add pork and cook until lightly browned. Add chili powder and mix well. Add tomatoes, beans, water and season to taste with salt. Cover and cook gently 30 to 45 minutes. HOT TAMALES (Makes 40 small tamales) 1 1/2 pounds beef stew meat 2 1/2 pounds chicken pieces Water Salt 1 clove garlic, crushed 1small onion, sliced 1/4 cup vinegar 1 cup minus 2 tablespoons catsup 1 teaspoon sugar 2 tablespoons chili seasoning mix 6 tablespoons chili powder 3 cups cornmeal Cornhusks, soaked until soft, drained and dried, or 7-by-5-inch sheets of parchment

Place beef and chicken in separate saucepans. Cover each with water and season to taste with salt. Add crushed garlic clove to beef and sliced onion to chicken. Bring to a boil, cover and cook until tender. Drain beef and chicken, reserving broths. Shred chicken Chop beef fine. Place beef in saucepan with vinegar, catsup, sugar, 1 teaspoon salt, chili seasoning mix and 4 1/2 tablespoons chili powder. Add enough broth to moisten slightly.

Measure 6 cups combined chicken and beef broth. Strain place in large saucepan and add salt to taste and remaining chili powder. Bring to a boil and stir in cornmeal. Cook slowly 15 minutes, until very thick, and remove from heat.

For each tamale, place 2 to 3 tablespoons mush mixture in center of cornhusk or parchment square. Press thin. Add a heaping tablespoon beef mixture and one or more chicken slivers in center. Roll husks or fold parchment and tie. Steam over boiling water 1 hour. When thoroughly cooked, store in refrigerator. Reheat by steaming or in top of double boiler.