Ralph Nader wrote to several large supermarket chains last year asking that they stop selling apples treated with daminozide, a farm chemical shown to cause cancer in laboratory animals. Four grocery chains, plus several apple juice and baby food companies agreed, and turned to suppliers who grew apples without daminozide. Meanwhile, the chemical is still on the market.

Thus, in the case of Alar, the trade name for daminozide, organized consumer pressure brought about stricter accountability than the government has yet required. It showed how in some cases the marketplace can move faster than the bureaucracy.

A study published two weeks ago by the National Academy of Sciences, which reported that current government regulations should be significantly improved to better protect the food supply from carcinogenic pesticides, raises the debate of what consumers can do -- both personally and collectively -- to bring about change and reduce their own risks.

The report picked 15 foods estimated to have the greatest potential risk. It did not imply that these 15 foods are actually dangerous as they are currently grown and marketed, but that regulations left them with the greatest allowable risk. In the case of tomatoes, for instance, not only are they widely consumed, but more carcinogenic fungicides are approved for them than for any other food. However, it is unlikely that all of those fungicides would be used at one time.

NAS used the worst-case scenario that assumed that pesticide residues were present in foods at the maximum tolerance level, that 100 percent of the acreage of the crop was treated and that exposure occurred over a 70-year lifetime.

The report "is not a food safety issue," said committee member Donald Bissing of FMC Corporation, a manufacturer of agricultural machinery and chemicals; rather, the numbers were meant to identify regulatory priorities.

While the public "shouldn't stop eating tomatoes," said Richard Wiles, project officer for the NAS study, "people should be concerned." Wiles said that the fundamental problem is that the regulatory system perpetuates exposure to chemicals that are more hazardous than many safer alternatives.

There are only bits and pieces of data on actual pesticide residues in food as consumed, although more is surfacing as a result of the NAS report, according to Wiles. The most comprehensive information to date is the Food and Drug Administration's Total Diet Study, which involves the analysis of 234 foods, prepared and cooked as consumers actually eat them. In 1986, pesticide residues on these foods were well below acceptable daily intakes, according to Ellis Gunderson, chemist with the FDA's Division of Contaminants Chemistry. The study is limited, however, because it does not analyze every pesticide for which there is a regulated tolerance.

Even so, environmental groups have long criticized the methods by which tolerances are set. Almost half of all registered pesticides lack fundamental safety studies on which tolerances are set, a factor which leads advocates to believe that their risks are greater than currently known.

At least nine fungicides presently used are known to cause tumors in animals, according to EPA. For example, one widely used one, mancozeb, was estimated by EPA to have a risk of 2.2 cancers per 100,000 people, when it breaks down to a more dangerous chemical in the body.

From a consumer standpoint, it is virtually impossible to determine what pesticides have been used on a particular food, given the complexity of the distribution chain and fact that although numerous chemicals are often registered for a given crop, they may not actually be employed. There are striking regional differences in pesticide use, too, depending on climate and geography. The majority of fungicides used on tomatoes, for example, are applied by growers in the Midwest, East and Southeast, even though less than one-third of tomatoes are grown in these regions, according to the NAS report. Similarly, potatoes from Idaho have fewer fungicides applied to them than those from Maine.

Unfortunately, since there is very little information disclosed at the point of purchase, "protecting yourself from pesticide residues is not a self-help project," said Ellen Haas, executive director of the consumer group Public Voice for Food and Health Policy. Haas recommends that consumers be wary of "perfect-looking produce," which may have been sprayed liberally to kill insects that would mar the look of perfection and to be aware that imported produce may contain pesticides either banned in the United States or above domestic tolerance levels.

In addition, everyone agrees that washing food is likely to get rid of at least some residues. "We can't wash everything all off of anything," said Wiles. "But keep washing. Wash and write your congressman."

While the EPA has very little data on what home washing actually does, Chuck Trichilo, chief of the agency's residue chemistry branch, said that warm water may be better than cold, and that mild soapy water may remove even more residues. Trichilo, who says he uses warm water and Ivory soap to wash his own produce and peels his apples because he doesn't want to eat the wax, emphasized that thoroughly washing off soap is crucial. (The June issue of the EPA Journal recommends that consumers scrub fruits and vegetables with a brush and peel them if possible; it does not recommend soap. It also suggests discarding fats and oils in broths and pan drippings, since residues of some pesticides concentrate in fat.)

When it comes to rinsing produce after it is harvested, not all crops are washed since water may decrease their lifespan, according to Claudia Fuquay, director of National Agrichemical Program of the United Fresh Fruit and Vegetable Association. Fuquay said that most head lettuces are not commercially washed; however, their outer leaves are generally removed for handling and asthetic reasons before they are packed. Tomatoes, citrus and most tree fruits are washed, according to Fuquay.

As for washing before produce is processed, research performed by the National Food Processors Association found that 71 percent of parathion residue on spinach was removed by washing and blanching using factory sprays and equipment. NFPA concluded that the nature of the chemical and the crop on which it is applied affect the amount of pesticide that will be removed.

Unfortunately, some pesticides just won't wash off. Systemic pesticides, which lodge inside a food, cannot be removed by rinsing. Benomyl, a fungicide used on tomatoes, and daminozide in apples are two examples of systemic pesticides.

Waxes, which are often used on the surface of fruits and vegetables, frequently are mixed with fungicides, according to Sandra Marquardt, resource information coordinator with the National Coalition Against the Misuse of Pesticides. Both the wax and the fungicide are difficult to remove, Marquardt said.

Determining pesticide residues in processed food is another issue. With some foods, such as tomato paste and dried fruit, pesticide residues actually become higher after the food is processed because these products are concentrates.

According to a study from the National Food Processors Association, tomatoes containing 1.76 parts per million of benomyl after harvest were reduced to .31 ppm after commercial washing. When the tomatoes were turned into paste, the residue increased to .57 ppm.

The increase, however, was still 1/10th of the residue permitted in the raw agricultural product, according to Dennis Heldman, executive vice president of scientific affairs at NFPA.

Whatever the types and amounts of pesticide residues in food and whether or not they pose a health threat, it is clear that consumers are concerned about them. According to a recent survey conducted by the Food Marketing Institute, a trade group of supermarket chains, 76 percent of shoppers rated pesticide residues in food a "serious hazard." No other food and health issue was rated as serious a hazard by as many people.

Consumer groups, who have hounded the EPA and FDA for years to better regulate pesticide residues in food, are now trying to mobilize this concern by putting the pressure on growers, manufacturers and retailers to offer pesticide-free alternatives.

Although the committee makes no recommendations for or against organic agriculture, Wiles of NAS said, "as a consumer you're helpless unless you manipulate the market. The best weapon you have is your money."

"So much time and effort goes into lobbying to get a certain chemical banned," noted Ben McKelway, associate director of the recently formed Americans for Safe Food. While the group tries to keep track of regulatory efforts, the major focus, he said, is in stimulating demand for pesticide-free foods.

ASF, coordinated by the advocacy group, Center for Science in the Public Interest, is setting up local action groups throughout the country to encourage interest in organically grown foods.

McKelway said the local consumer leaders will "very politely urge supermarket buyers to seek out organic products to offer an alternative." The whole process is expected to be taken, he says, "on a positive, cordial basis."

Organic foods cost about 10 to 30 percent more than conventionally grown food, according to McKelway, but he says "once it gets rolling, we hope the price differential would decrease. Right now consumers must pay a premium for safer foods."

According to Karen Brown of the Food Marketing Institute, a number of supermarket chains have expressed a willingness to provide organically grown foods, but she noted they face several obstacles. One is the problem of availability.

Larry Johnson of Safeway said that the chain has had "some in-house discussion" about organic produce but that the biggest problem is that the quantity available doesn't match the chain's needs. Johnson did say, however, that organic produce could be promoted on a select store basis or as a specialty item.

Sue Challis, spokesperson for Giant, said the chain has investigated buying organic produce, but has found similar supply problems. Additionally, "if we had consumers calling us every day and asking for organic produce, it would a different story," Challis said.

Richard Koslow, co-owner of Organic Farms, a Beltsville wholesale company that sells organic goods throughout the East Coast, said that the company has had ongoing discussions with large supermarket chains. Aside from concerns over adequate consumer demand, Koslow said, the companies are reluctant to change a "very ingrained pattern of behavior."

Another problem that supermarkets face, noted Brown, is certifying that the food was actually grown without chemicals. McKelway is well aware of the problem of certification: "There's a potential for abuse there, and I just hope that it's not too common." Several months ago, Giant Food was preparing to carry so-called "natural beef," but canceled the program at the last minute after discovering the cattle had been treated with antibiotics.

One problem is that there is no national definition of organic. McKelway hopes that differences among farmers can be ironed out enough to win support for a bill in Congress for a definition. Several states already have definitions, but they are not all the same.

Marquadt of the National Coalition Against the Misuse of Pesticides said that consumers should educate themselves about the problems of pesticides, support the organic movement and write to their representatives on both the state and federal level "to let them know that they don't want to take it anymore."

Freelance writer Patricia Picone Mitchell contributed to this report.