"Nine in 10 shoppers who eat organically grown produce rank it as excellent or good in terms of . . . nutritional value," according to a survey sponsored with the help of the Food Marketing Institute. But do organically grown fruits and vegetables have higher levels of vitamins and minerals than conventionally grown produce?

While many people might think so, "it's a very, very difficult question to answer," says William Lockeretz, a professor at Tufts University's School of Nutrition Science and Policy, who specializes in alternative agricultural methods. "There has been a fair amount" of research, he notes, "but there isn't any conclusive picture that emerges. The only tendency that seems to be emerging more or less consistently is that organically grown food often shows a higher vitamin C content. But even with that, you don't get the [same] result every time. The prevailing thought is that there's no clear difference shown" in the nutrient content between foods grown with different methods.

One of the problems in looking at the issue is that many of the studies have been "very crude," according to Joan Dye Gussow, a professor emeritus at Columbia University Teachers College in New York, who has been studying organic foods for more than 30 years. But it's not necessarily the fault of sloppy researchers. It's hard to conduct a finely executed study on the subject, she says, because there are so many variables influencing foods' nutrition content. Among them: the mineral composition of the soil, the exposure to sunlight, the substances used as fertilizers and the particular variety of fruit or vegetable being examined.

But Lockeretz, Gussow and others feel that not having a firm answer on whether organically grown foods have higher levels of nutrients than other foods isn't important. "The United States is already well-fed," Lockeretz points out, "as are other Western nations where people buy organic foods. Consumers of organic foods [in particular] are not hurting for this or that vitamin" because they tend to eat quite well in the first place.

Instead, advocates of organic foods argue that these products are necessary because of their effects on the environment. "The environmental benefits of organic farming far outweigh any nutritional benefits," notes Molly Anderson, acting director of the Tufts Institute for the Environment. "Probably the strongest environmental benefit [of organics] is in building soil and improving soil quality. The United States, and the rest of the world, is losing topsoil," she points out, "and topsoil is irreplaceable." Indeed, she says, letting topsoil erode is akin to "taking out $100 bills from a bank account, standing on a tall building, and letting them blow away in the wind."

Some of the ways in which organic farmers prevent erosion of topsoil, which is the best type for plant roots and plant nourishment and therefore for ultimate food production: putting a high priority on keeping the ground covered for most of the year, say, by planting winter cover crops as well as summer crops (crops keep the soil from "slipping"); rotating row crops like corn with closely grown crops like grass or clover, which also helps hold the soil in place; and adding organic matter to the soil, which improves soil structure and texture.

Beyond soil health, proponents of organic farming claim that it promotes greater biodiversity. In conventional agriculture, farmers depend mainly on seeds that produce crops that ripen simultaneously and therefore can be harvested more efficiently. But this approach cuts down dramatically on the variety of fruits and vegetables available. Consider that there used to be more than 400 types of tomatoes. Now there are several dozen. If a plant disease hits, there's less chance that a resistant variety exists to fight it off.

Another benefit of organic farming is protection of the water supply. Because organic farmers don't use toxic chemicals that are found in many pesticides, there is no runoff of such toxins and the nearby water remains cleaner. Organic alternatives to synthetic pesticides also provide more protection for farm workers and endangered species of animals.

Ironically, what seems to fall low on the experts' list of concerns is pesticide poisoning of the consumer. "Poisoning by pesticide is not that big a deal in the United States," says Tufts's Lockeretz. "Standards on pesticide residues are stricter than in many other countries." Imported food may not be subject to the same strict standards, he concedes, but even so, he doesn't feel there's much risk of sickness from pesticides--aside from farm workers who may be exposed to high levels of these toxins.

Anderson shares this view. "Pesticide contamination is a really, really serious problem for a lot of ecosystems," she says, but "the dangers from pesticide residues are very small to the average consumer." That is, the pesticide issue is much more critical in terms of contaminating the environment than in terms of, as she puts it, "which apple you eat."

In other words, the choice of organic foods may not have an effect in your own kitchen. But Lockeretz likens it to choosing between a garment made in a sweatshop and a garment made under better conditions. "The sweatshop clothing could be just as good," he says, "but you don't want it" because of the way it was made, the exploitation involved. It's the same with organics. You're not necessarily getting "a better product," he says. "But the product was made better," without exploiting the land, farm workers or wildlife.

Advocates also argue that buying organic has implications for the health of future generations. When people think about things like sustaining the Earth's topsoil, says Kate Clancy, who directs the Agriculture Policy Project at the Greenbelt-based Henry Wallace Institute for Alternative Agriculture, they're "looking into the future--for their grandchildren's health." Without soil health, she says, "you can't grow things."

CAPTION: Researchers find it difficult to compare the nutritional value of organic and non-organic foods.