ASK THE New England cook of 100 years past what was for supper on Saturday night, and she would check your forehead for fever. Saturday night supper was for supper, of course.

The menu for this weekend repast consisted of what one writer woefully calls the "inevitable" baked beans and brown bread, the latter a chewy, wholesome sweetbread, studded with either raisins or bits of apple and then steamed.

Here is a basic worthy of a return trip. The bread, a combination of three grains (cornmeal, rye and whole wheat or graham) mixed with molasses and soured or buttermilk, gets its moisture from steaming, not from the addition of fat.

Steaming can be done handily in the modern crockpot, which maintains the water level so the bread does not need to be watched. If one of these is not available, the batter-filled tin cans can rest on a rack in a Dutch oven, but the water should be checked periodically and replenished.

The batter is simplicity itself to make, but requires a kitchen stocked with grains. Substitutions can be made easily, if you keep the proportions intact; use at least two different varieties of flour for contrasting flavors.

The bread relies on the reaction between baking soda and an acidic liquid to make it rise. While buttermilk is the usual wet choice, you can substitute soured milk or fruit juice. To make soured milk, add one tablespoon of vinegar or lemon juice to each cup of milk.

Raisins are the traditional lily gilding -- chopped raisins, if you come from Cape Cod -- but nuts, coconut or any chopped fruit make good additions. Since the bread steams so long, it is better to use dried fruits which plump out during the cooking than fresh fruits, which dissolve with the steam.

Once the batter is mixed, use it to fill greased tin cans two-thirds full. One-pound coffee cans are usually recommended, but the small one-pound vegetable or fruit cans make a tidier loaf. There are special brown bread cans in some families, and at least one New England food authority recalls the bread being baked in a five-pound lard can with the word "Swift" on the side in raised letters.

Cover the tins with foil -- purists insist the foil should be tied in place -- and place them on a rack in either a crockpot or kettle. Pour water around the cans until it comes halfway up the tins, cover the pot and bring the water to a simmer (set the crockpot to "high").

Length of cooking varies widely with the pot used and the size of the can. You can expect it to take a minimum of three hours, and probably four, to cook the smaller cans; the filled coffee cans may take five hours to finish. A few minutes more cannot hurt; better to err on the longer side than the short.

After at least three hours of cooking, check the bread by removing the foil and inserting a knife all the way through the middle. If the knife comes out clean, the bread is done.

Let it rise five or 10 minutes outside of its steam bath, and unmold by running the knife around the edges, and turning the can upside down. If the bread won't budge, open the other end with a can opener, and use the lid to push it out.

Occasionally you will get a loaf that is cooked through, but slightly soggy around the edges. You can dry it out in a 400-degree oven for about 10 minutes, for a prettier effect.

The following recipes adhere to the brown bread principle, and should warm your family on Saturday or any other night: BOSTON BROWN BREAD 1 cup corn meal 1 cup rye flour 1 cup whole-wheat or graham flour 1 1/2 teaspoons baking soda 1 teaspoon salt 3/4 cup molasses 2 cups buttermilk or sour milk 1 cup raisins

Mix dry ingredients in large bowl. Mix together molasses and buttermilk, and add this to the dry ingredients, stirring just to blend (like you would for muffins). Add the raisins, if desired. Spoon into two greased 1-pound coffee cans or three 1-pound vegetable cans (will only fill 2 1/2 of the smaller cans), and steam. TANGY BROWN BREAD

My family called this "better than Boston" without knowing its secret ingredient! 1 cup corn meal 1 cup rye flour 1 cup whole-wheat flour 1 1/2 teaspoons baking soda 1 teaspoon salt 3/4 cup molasses 2 cups tomato juice 1 cup raisins

Mix dry ingredients in large bowl. Mix together molasses and tomato juice, and add this to the dry ingredients, stirring just to blend. Add the raisins, and steam. STEAMED ORANGE LOAF

Almost a cake, this makes a good breakfast loaf! 1 cup corn meal 2 cups unbleached white flour 1 1/2 teaspoons baking soda 1 teaspoon salt 1/2 cup honey 1 1/2 cups orange juice 1/2 cup black walnuts or shredded coconut (optional)

Mix dry ingredients in large bowl. Mix together honey and juice, and add to dry ingredients, stirring just to blend. Add nuts, if desired, and the grated peel of one orange. Spoon into cans and steam. APPLE OATMEAL BREAD

The absorbent oatmeal makes this a slow-cooking bread; steam at least five hours. 1 cup oatmeal, uncooked 1 cup whole-wheat flour 1 cup unbleached white flour 1 1/2 teaspoons baking soda 1 teaspoon salt 1/2 cup honey 1 1/2 cups buttermilk 1/2 cup chopped dried apples

Mix together dry ingredients in large bowl. Mix honey with buttermilk, and add to dry ingredients, stirring just to blend. Add apple bits. Spoon into cans, and steam.