Americans live longer than ever before, but they still worry about the safety of the food they eat. It might be more appropriate if they worried more about the amount of food and the kinds of food they eat.

Sad to say, most Americans are overweight and underexercised.More and more scientists are finding that the problems in food safety are not pesticides or other chemicals used by farmers and ranchers.

The real culprits are high-fat diets, overdoses of sugar, natural toxicants that plants produce to protect themselves, chemicals in packaging materials and microbes that get into food at some point in the food delivery chain - at the farm, the processing factory, on a truck or rail car or on the kitchen table.

When it comes to food safety, it is amazing what selective attention the public pays to risks. For instance, the health effects of smoking are dramatic, well-known and well-publicized. But people continue to smoke.

Von Mendenhall, professor of nutrition and food science at Utah State University, estimates that 25 percent to 40 percent of cancer cases could be avoided if people stopped smoking.

The words "chemical," "additives" and "processed" are unpopular words. But Mendenhall points out, "Foods consist of chemicals. Food is simply the chemicals we eat."

We need 52 different chemicals - nutrients - to grow, repair and sustain our bodies. Thousands of other chemicals are present in food, Mendenhall says. Some may be incidental, others are added for various purposes such as flavor, color or to maintain food quality and stability.

When we eat, we also consume microbes, natural plant and animal regulator substances such as hormones and enzymes and natural toxicants.

Toxicologist James Seiber, associate dean of the College of Agriculture and Environmental Sciences and the Agricultural Experiment Station at the University of California-Davis, believes America's food is definitely safe.

"The real villains in cancer are cigarettes, alcohol and high-fat diets, which go unchecked while we focus unnecessarily on such things as pesticides," he says.

Speaking recently about food safety and chemical contamination at the second annual Land Grants Days conference at Utah State University in Logan, Seiber said regular monitoring of food by the Food and Drug Administration shows pesticide residues far below the legal limit.

"The real problem is the generally negative attitude the public has toward chemicals of all types and the public's inability to distinguish between relatively safe and relatively hazardous chemicals."

Seiber says we should be constantly vigilant about toxins in foods at high enough levels to cause harm, but the concept of "zero tolerance" levels is a straw man. "In the real world, every food is contaminated with low levels of every chemical," Seiber said.

"The difference between finding a finite residue and `no detectable' residue lies in the sophistication of the analytical method."

Pesticide usage is being reduced in mainstream production agriculture by such techniques as biological control, cultural practices and crop rotation.

But, Seiber says, "it is preposterous to think that in a few years we will be able to turn around a production system which has served agriculture so well for more than 50 years - during a time when the largest yield gains in history were achieved - and replace it with non-chemical farming techniques.

"Furthermore, there is no evidence that food would be safer if this were achieved."

Many scientists contend that:

- If fungicides are not used, the level of fungi - many of which produce cancer-causing chemicals - would increase.

- If more insect damage is tolerated, disease organisms might be better able to gain entry to foods.

- With new resistant crop varieties, natural toxicant levels may be higher since, scientists say, there must be a reason why these new varieties, which require less chemicals, are "resistant."

It is quite possible that pesticides and other farm chemicals are not nearly so damaging as many people believe. Instead, an intelligent, optimum use of chemicals should be applauded for producing not only the most abundant supply of food in the world, but the safest food.

Instead of worrying so much about pesticides and farm chemicals, we should slim down by exercising, by eating the amount of calories we need, and by cutting down our social eating. And we should pay attention to the scientific evidence that smoking, drinking and drugs are bad news.