Americans are talking about changing their eating habits, but only a small percent of them are translating their talk into action. Serious athletes, particularly runners, seem to be the only exception.

Those are the findings of two in-depth surveys done last year, one of which concluded that among most Americans, interest in nutrition "cannot automatically be translated as a commitment to . . . improved nutrition habits."

This despite the fact that in the second study, 92 percent of those surveyed understood that: "When people want to be physically fit they also are more careful about how much they eat."

The nutrition survey, conducted for Woman's Day Magazine by Skelly, Yankelovich and White, ascribes the interest in good nutrition to "the mounting national commitment to physical fitness and well-being. Improved diet and physical fitness go hand in hand - and consumers themselves point to interest in physical fitness as the major factor creating the growing concern with nutrition. . ." But only a minority (24 percent) feel strongly about "eating what's good for you."

These findings appear to agree with the conclusions reached by Louis Harris and Associates in a fitness survey conducted for Perrier.

The Harris study of 1,510 adult Americans shows that 59 percent of them engage in some sort of physical activity, but only the 15 percent classified as "high active" have made appreciable changes in their diets. High actives spend at least 306 minutes a week on vigorous activity and burn, on average, 1,500 calories per week exercising. "Moderate actives" spend 204 minutes; "low actives," 150 minutes and "not actives," zero.

A 150-pound person between five and six feet tall would have to spend from a high of 144 down to 129 minutes running while he or she would have to bowl anywhere from 529 to 474 minutes to burn 1,500 calories.

It is these high active persons who, according to the study, "become more conscious of their weight, and what they eat." They also have a better understanding about diet and exercise. They eat far more fresh vegetables and fruit, milk products, poultry and fish, breakfast cereal and drink more water than the moderate or low active groups, or the non-actives.

When the groups are broken down even furthru, to include the three levels of activity plus runners, there are even great differences. Participation in athletic activity affects the diet of 60 percent of the runners, 42 percent of high actives, but only 32 percent of the total active group.

Obviously runners consume more liquids than any of the other groups. This includes not only water, but fruit juices, mineral supplement drinks, beer and hard liquor. Runners have also surpassed all of the other active groups in their increased consumption of vegetables, dairy products, whole wheat products, vitamins or minerals, fish, red meat, poultry, salt, diet soft drinks and artificial sweetners, yogurt, bread and a category called "health foods in general."

The only category in which they consume less is one classified as "junk food."

While these consumption patterns indicate some awareness of good nutrition, they also indicate some ignorance. The safety of artificial sweeteners is under a cloud. Increased salt consumption by athletes is not recommended by sports medicine experts who caution that it can be quite dangerous. these experts also dispute the value of the mineral supplement drinks such as Gatorade and ERG. The need for vitamin and mineral supplements is also the subject of great controversy.

Since runners have increased their consumption of wine, beer and hard liquor to a greater extent than any of the other active groups, presumably it is in their quest for more liquid, or as one "high active" racquetball player commented, "as compensation. If you work hard, you treat yourself."

When Linda Smith, a consultant at the Washington-based Community Nutrition Institute, surveyed runners who subscribe to a runners' journal, her result were somewhat the same. Smith wrote: "Over 90 percent of the 249 readers who responded to a survey reported that they, too, had changed their eating habits." But Smith's respondents appeared to be a bit more knowledgeable about nutrition.

Smoking patterns follow eating patterns; overall, activists are as likely to smoke cigarettes as non-activists, with little difference seen between the high active group and the others: 60 percent of them do not smoke. When runners are separated from everyone else, the figure for non-smokers rises to 76 percent. Just behind runners are walkers, tennis and racquetball players: 67 percent of them do not smoke.

Asked to comment on several myths about exercise, the more active people scored better. Among non-actives 36 percent believe the key to staying fit is not exercise, but to control how much you eat.Only 15 percent of the high actives believe that shibboleth: 25 percent of the low actives. Thirty-eight percent of the non-actives believe people who exercise work up big appetities and then eat too much, making exercise useless: Only 10 percent of the high actives believe that.

Few active participants, no matter the level, see a loss of weight as a benefit derived from their activity. The majority of them just feel healthier in general.

The overall effect of exercise, according to the study "probably does not result in reduced appetite." The fact is, the majority of high actives neither gained nor lost weight. Among moderately active people 45 percent stayed the same; 32 percent lost weight and 23 percent gained.

The study concludes: "On a weight basis, the more people exercise, the more their weight is controlled, as the survey shows clearly. In fact one cannot be involved in a regular exercise regimen and overeat. The exercise is almost impossible to keep up."

But it is not clear from the study whether activists eat less than non-activists. Whether activist or not, the majority (55 percent) feel they eat the right amount of food - a surprising finding since the majority of Americans are overweight.

The conclusions of both studies are essentially the same: Americans still have a lot to learn about nutrition and fitness. People perceive their importance, but most of them haven't translated this knowledge into action, often because their knowledge is incomplete and flawed. Said the Harris survey: "What people lack, at this point, is a clear understanding of the nuts and bolts of fitness - exactly what is required to become and stay fit.

"To a large degree, this is because many people - activists and non-activists alike - are poorly informed. . ." CAPTION: Illustration, no caption, By Cameron Gerlach for The Washington Post