IN FIGHTING FAT, LIGHTEN UP ON INGREDIENTS, METHODS : RULE-BENDING, CALORIE-CUTTING ADVICE.

``Rules are made to be broken!'' If you're fat-fighting, ``breaking the rules'' is better cooking advice than ``follow the directions.''

Omitting fattening ingredients and cooking techniques can save you calories, usually without compromising the results. Leaving out the oil, omitting the sugar, cutting down on the butter or intentionally bypassing the prebrowning step, can save time as well as calories.

Casserole recipes that call for frying meat in oil will be lower in fat if you brown meat under a preheated broiler on a perforated pan. Drain well to eliminate as much fat as possible.

Onions will have more onion sharpness, no fat and fewer calories, if you don't brown them first.

Plain tomato juice, simmered down to a sauce consistency, can stand in for tomato soup or tomato sauce (which may contain fat and fillers, starches and sugars). Use low-salt juice, if available, otherwise omit adding more salt.

The fat, butter or shortening called for in muffin, biscuit or quickbread recipes can be cut in half or eliminated altogether. Add more milk or water to get the right consistency. Mashed or overripe bananas added to the batter provide some of the buttery-mouth feel that might be missing in nonfat or low-fat sugar.

Evaporated skim milk, fresh nonfat milk or fruit juice can be substituted for cream or evaporated whole milk called for in pumpkin pie filling recipes. If you substitute fruit juice, you also can cut down on the sugar.

``Creamed'' soups that call for the addition of milk, will be just as creamy if you substitute nonfat milk. Or try half nonfat milk and half water.

Sour cream - the dairy regular high-fat kind - can be replaced by its low-fat or fat-free alternative in any recipe. Not available? Use plain, preferably nonfat yogurt, drained in a coffee filter paper to sour cream consistency.

You also can replace sour cream with blender-whipped cottage cheese diluted to sour creaminess with a little water and lemon juice. Any dip mix that calls for sour cream can be decalorized with these sour cream substitutes.

Cocoa powder can substitute for chocolate. And, regardless of what your cookbook tells you, it's not necessary to add fat when you replace baking chocolate with powdered cocoa. Use three teaspoons of cocoa powder in place of one ounce of unsweetened chocolate.

Substitute four egg whites for two whole eggs. Or use egg substitute.

Revise directions

Ignoring the directions can work with packaged mixes, too. If the back of the box calls for the addition of unwanted calories, why follow the command blindly? Ask yourself if this ingredient is really necessary. Most often, you'll be delighted to find that the ingredient wasn't really needed and you have saved several hundred calories.

If you're afraid to omit the ingredient, try cutting the amount in half. If the recipe still succeeds, next time you can reduce the amount even further and perhaps eventually risk leaving it out altogether.

Some examples:

Rice mixes often suggest that you first brown the dry rice in fat or oil. This step can be omitted. You also can ignore the suggestion that you add one to two tablespoons of butter to the mix. Or you can substitute margarine or diet margarine.

Dressing and stuffing mixes usually call for the addition of water and fat (butter, margarine, oil or shortening), but the fat isn't necessary. Leave it out. You can improve the flavor of packaged mixes by substituting canned or homemade fat-skimmed broth for water.

Sometimes more is less. Try adding more onion, celery, carrots, parsley and other fresh vegetables to rice or stuffing mixes or meatloaf recipes. You'll stretch the number of servings and make each serving lower in calories, while boosting nutrition and natural fiber content. Because fresh vegetables have lots of natural moisture, reduce the amount of water added to the mixture.

Change the ratio

Dry salad dressing mixes direct you to combine the mix, vegetable oil, vinegar and water. You can cut calories by changing the ratio: less oil, more water and vinegar.

Marinades and basting mixes often call for the addition of large amounts of oil, even though the oil adds no flavor and does nothing to promote tenderness. Cut down or eliminate the oil. To make up for the missing oil, increase other liquids. Water, unsweetened fruit juice, tomato juice or dry wine can be used in place of the oil. Most steaks, chops and burgers have enough fat of their own, so no added oil is needed.

Take directions ``lightly''

Sauces and salad dressing based on mayonnaise can be cut in half calorically simply by substituting the low-fat (light) kind in place of the real (real fattening) version.

Light, low-calorie and low-fat bottled commercial salad dressings can stand in for the more fattening brands in barbecue recipes that call for salad dressing as a marinade. Try beef or chicken marinated with low-calorie French or Italian dressing.

Pancake and waffle mixes that call for the addition of milk, eggs and oil can be calorie-reduced, if you simply omit the oil. You can cut calories further by substituting nonfat milk for whole milk (half milk, half water). Or simply substitute water for milk. Whole eggs can be replaced by cholesterol-free substitutes or egg whites.

Molded desserts and salads that call for sugary gelatin dessert mixes can be made with sugar-free gelatin mixes. Or make them naturally healthy and sugar-free by substituting plain gelatin and boiling fruit juice. Use one envelope of plain gelatin and two cups of boiling juice in place of the mix and boiling water the recipe calls for.

No acceptable-tasting sugar-free pancake syrups on the market? Use one of the aspartame-sweetened sugar-free jams, thinned with some water or fruit juice, to make a fruit-flavored topping. Try the strawberry or raspberry, then top it off with some fresh berries. Sliced bananas can replace butter.