GROWTH-ORIENTED food companies struggle against a limitation unknown to most other industries. As auto and electronics manufacturers discovered long ago, Americans possess a virtually insatiable desire for their products. A one-car, one-TV family seems about as rare today as a household without a flush toilet.

But pity the poor food industry. People, alas, do not have insatiable appetities. In fact, an individual's food needs are easily defined and rarely exceed 2,000 to 3,000 calories a day. This natural "limit to growth" poses a stiff chanllenge to marketers, scientists and the top executives of food companies. How can companies entice consumers to buy more and eat more, but stay hungry?

one solution is to alter the composition of foods. Since one of the basic limits to eating is set by the number of calories, companies can hike sales valume of decreasidng the caloric content contained in each package. Noncaloric sweeteners, such as saccharin, are vital to this strategy. No longer must the public settle for ordinary tap water to quench a thirst. Now calorie-free soft drinks wet the whistle and increase the gross national product at the same time.

Reduced-calorie foods are a boon to the bottom line. Manufacturers replace expensive ingredients with saccharin or water, and still charge about the same price. The soft drink industry, for instance, charges as much for its diet sodas as the regular sodas, even though the low-calorie drink is much cheaper to produce. The diet soda ripoff amounts to about $300 million a year.

What saccharin does for soda pop, low-calorie carbohydrates often do for solid foods. Dietary fiber (or "roughage") has bulk, but few calories. It is absorbed poorly into the body. Several years ago, ITT-Continental Baking introduced a product -- Fresh Horisons bread -- that uses a poor form of dietary fiber. The label describes the fiber as derived "from a naturally abundant wood source," which we all know as trees. The company replaces some of the flour with wood cellulose and charges two to three times as much as a regular super-market loaf for the product. Since then, Continental's methods have been copied by others.

Don't misunderstand, however: Roughage is no match for saccharin when it comes to extending hunger. Roughage absorbs water and conveys a sense of satiety in the stomach. But the feeling of fullness passes rather rapidly. It's not long before you want to belly up to the kitchen table again.

Air and water are popular food stretchers, largely because they are so cheap. Whipped butter contains 50 percent air and costs about 25 percent more than an equal weight of regular butter. Air is also used to produce ice cream that evaporates as much as it melts in the cone. Some brands barely qualify as ice cream at all, hovering just over the legal minimum weight of 4.5 pounds per gallon, or about one-half air.

Water offers the food technologists several lovely properties: It is cheap, noncaloric, and has weight and volume. Diluted "low-calorie" beers are basically watered-down versions of regular beer (though different brands are produced by different; processes). Selling air and water at a dollar or so a pint is just plain smart business.

One of the cleverest discoveries to emerge from the chemical laboratories in recent years is a procedure for producing resin-bound food additives. Scientists, aware of the controversies surrounding food additives that cause cancer, have figured out how to attach these coloring and other substances to huge molecules which pass right through the gut. The additives are never released into the bloodstream to do damage. (One hopes that they do not damage the gastrointestinal track, either.) If this process becomes commercially wide-spread, it may mean that entire foods will be modified to prevent their absorption into the body.

Where this search to break the calorie barrier will end, no one can tell. Will some food packages recommend that their contents be smelled, chewed and tasted, but not swallowed? Will wooden sticks be impregnated with flavorings so that we can suck on them all day and not ingest any calories or bulk? Will harmless parasites be developed and introduced into our stomachs or intestines to help burn up a meal's calories? Tune in later to find the answers. Eating in the year 2000 may offer adventures that are today just dreams in a chemist's mind.