If you drink coffee and eat imported foods, you are risking the unknown. This, at least, is one conclusion to draw from the Natural Resource Defense Council's new report, "Harvest of Unknowns: Pesticide Contamination in Imported Foods."

The NRDC, a well-known environmental protection organization headquartered in New York, focuses in the report on coffee, which it says contains residues of such banned pesticides as Aldrin, BHC, Chlordane, DDT and Lindane. These and other chemicals found in coffee cannot be used as pesticides in the United States because, among other things, they are carcinogens or cause genetic damage or birth defects.

U.S.-banned pesticides are often sprayed indiscriminately in the Third World, says the report. Every sample of coffee beans the NRDC tested was contaminated with residues of such pesticides. But in many cases, the residues were minute, according to the report, written by Shelley A. Hearne..

For instance, the levels of some pesticides detected by NRDC with extra-sensitive probes were one-tenth to one-hundredth the size of levels that, even if detected, the FDA would consider unworthy of concern.

The question then is, are they dangerous, and how safe are imported agricultural commodities in the American diet? The Food and Drug Administration is charged with monitoring pesticides in food and maintaining the safety of our food supply.

"We do not know what the impact is on human health, based on the sparse information from the Food and Drug Administration's own data," says Karim Ahmed, NRDC senior staff scientist and director of research. Ahmed says he has cut his own coffee consumption from "heavy" to "moderate," and eliminated tropical fruits from his diet.

In order to make its own assessment of how contaminated imported food is, the NRDC contracted with an independent laboratory to test for pesticides in coffee. Why coffee? The nation's favorite hot beverage -- two cups a day per capita -- is also almost entirely imported from the Third World.

The NRDC tests essentially corroborated FDA's findings of the amount of coffee that was contaminated. Pesticides were in more than 30 percent of the samples. But when the NRDC switched to more sensitive probes, it found multiple pesticides in every coffee tested.

Additionally, after examining 1982 and '83 computer printouts from the FDA's food monitoring program, NRDC noted that ". . . many of the major food commodities imported into this country arrive with over half their shipments containing detectable levels of pesticide residues," and added that many of these pesticides are illegal to use in the United States. The NRDC implied in the study that contamination of food may also be more widespread than FDA's monitoring indicates and criticized the agency for failing to publish its monitoring results for the last eight years.

The real danger, says Ahmed, lies in the context that a lot of tiny risks throughout the food supply eventually add up. But we have no idea what the sum of them is, partly because FDA's monitoring is not comprehensive, says Ahmed. "We simply don't know the full extent of what's coming in."

Specifically, the FDA screens samples of imported foods with five "multiresidue" pesticide tests, but these pick up only about half of the 312 pesticides that have been registered for use in the United States. Some of these pesticides have been banned from use but have legal tolerance levels. For any given sampling of imported foods, FDA seldom applies more than two of its multiresidue tests.

Furthermore, as of 1979, according to the General Accounting Office, the multiresidue tests could not detect 64 of the 94 pesticides that were permitted on coffee in the major growing nations. The FDA was unable to comment on the GAO figures, but Bernadette McMahon of FDA said that the coverage of the multiresidue testing has increased by roughly one-third since 1979.

John Wessel, director of the contaminants policy staff at FDA, said this amount of testing is adequate, noting that there are certain pesticides that are expected on certain foods and the tests are used accordingly.

However, FDA's spot checks of food imports are rare. The agency tested only 14 samples of nearly 3 billion pounds of imported oranges in 1982-83, and only 42 samples of 2.3 billion pounds of coffee.

When FDA does find a problem, it's often too late to keep the contaminated food out of circulation. The problem is that many of the food imports would rot on the dock if FDA held them until the laboratory tests have been made. If FDA finds contamination, the food importer is bound to make a "good faith effort" to recall the food and is not penalized if this is done. The NRDC reports that about one-third of adulterated foods found are not successfully recalled.

The NRDC report accuses FDA of being extremely reluctant to block imports when it finds potentially dangerous levels of pesticides. A case in point concerns EDB, a fumigant commonly used to keep pests from entering other countries in international shipments of agricultural commodities and a potent carcinogen that was outlawed in the United States last year. As early as 1980, the Environmental Protection Agency had warned that "EDB poses substantial risks to public health." But NRDC says that only one shipment of oranges was tested for EDB, and despite "severe" contamination, no oranges were barred from entering the country.

Similarly, the FDA has not blocked imports of coffee containing detected pesticides for which tolerance levels have not been set. This is troubling to NRDC because "Not only are Americans exposed to potentially dangerous levels of chemicals, but the effectiveness of tolerance levels as trade barriers to adulterated food are undermined."

"Technically, this may appear to be a violation of the law, but I doubt we could sustain an enforcement action to take such adulterated food off the market," says Wessel. "The law also allows us to use our discretion," he says. "The fact that a tolerance hasn't been established doesn't mean it's going to hurt anyone."

Wessel also stated that the levels of some pesticides FDA has found on coffee represent environmental contamination rather than deliberate spraying, explaining that DDT is still found on U.S. crops although spraying hasn't occurred for 12 years.

Responding to charges that FDA's pesticide monitoring misses many pesticides used in the Third World, Wessel says, "We try to give the broadest coverage on commodities of dietary significance, and the pesticides used in foreign countries. Certainly we are not going to say we cover every pesticide, but based on what we are finding, there doesn't seem to be a major problem."

As for the charge that contaminated foods are often not recalled in time to keep them from being consumed, Wessel said the presence of contaminants in a single shipment is not going to hurt people.

Wessell concludes that "To say we are not adequately covering imports is grossly misleading. I would challenge NRDC to call Congressman "Kika" de la Garza D-Tex., chairman of the House Agriculture Committee . He's getting complaints from shippers all over Texas about our program."

One of the ironies of the pesticide problem is that many American corporations produce chemicals that are illegal to use here for sale abroad. Pesticides for export are specifically exempted from provisions of the Federal Insecticide, Fungicide, and Rodenticide Act that ban hazardous chemicals.

Less than a month after he took office, President Reagan rescinded an executive order by President Carter that would have tightened up on the practice of shipping hazardous products abroad. Under the Reagan administration, the United States has also been the only country in the United Nations to oppose a resolution calling for a comprehensive list of consumer products, pesticides, drugs and industrial chemicals that have been banned or restricted in at least one country.