Steve Taylor practically yawned when researchers at Pioneer Hi-Bred, the giant agricultural seed company, asked him in 1995 to study a new soybean they had invented. "I didn't think we'd find anything interesting," the University of Nebraska scientist recently recalled.

Little did Taylor know that his findings would help trigger a wave of anxiety over the safety of genetically engineered food in Europe, a wave that, years later, now threatens to engulf the United States as well.

Pioneer had spliced a Brazil nut gene into soybeans, creating a soybean that boasted a nutritious nut protein. Taylor's task was to find out whether the new soybean would cause allergies in people allergic to Brazil nuts, a potential danger because people with allergies to nuts wouldn't think to avoid soy.

The company had put just one of the Brazil nut's thousands of proteins into its new soybean, and the odds of that one causing the nut's allergies were incredibly low, Taylor said. So he could hardly believe it when first one test, then another, and finally a third indicated that the transferred protein was indeed a major cause of Brazil nut allergies.

In trying to build a better soybean, the company had made a potentially deadly one.

Pioneer immediately halted the soybean project. But Taylor's study lives on today as a symbol of everything that is both frightening and reassuring about genetically altered food, which has quietly made its way into nearly every American kitchen.

Frightening because the study proved that a gene-altered food could cause an unexpected and potentially fatal reaction.

Reassuring because the problem was detected before the product was marketed.

And symbolic above all because it was, and still is, one of the very few studies ever to look directly for any harm from an engineered food or crop.

That dearth of studies is the legacy of a U.S. policy that considers gene-altered plants and food to be fundamentally the same as conventional ones, a policy some Americans are starting to question.

It is also the legacy of the sheer scientific difficulty of conducting the kinds of tests that might assure people that engineered crops and food are safe.

And it is the legacy of broken promises by the Food and Drug Administration and the Environmental Protection Agency, both of which have said for the past five years that they intend to write rules to minimize the chances that gene-altered food will cause allergies or damage the environment.

"Americans are starting to realize that this process is not as all wrapped up as they thought it was," said Carol Tucker Foreman, a food safety specialist at the Consumer Federation in Washington.

Genetically engineered food, which is endowed with bacterial, viral and other genes not native to human food, has been widely, if mostly unknowingly, consumed in the United States since 1996. As far as scientists can tell, no one has ever been harmed.

But with evidence accumulating that the crops may be less environmentally benign than biotech companies had predicted -- most recently, gene-altered corn was found capable of killing monarch butterflies -- some Americans are reconsidering the technology's overall safety.

"I've had more calls about this allergy research in the past three months than I've had in the three years since we published it," Taylor said.

In Europe, that crisis of confidence already runs deep. Activists regularly vandalize newly planted plots of gene-altered crops. Major grocery chains have refused to carry engineered food. And food processors have begun to hire DNA fingerprinting labs to verify that their products are free of foreign genes.

The British Medical Association has warned that the technology may lead to the emergence of new allergies and speed the evolution of microbes resistant to antibiotics. Other groups worry that gene-altered crops may lead to the growth of insecticide-resistant bugs, or "superweeds" unfazed by herbicides.

In this country, gene-altered food is virtually unavoidable. About one-third of the corn growing in the United States is genetically engineered, mostly to exude its own insecticide, as is about half of the cotton crop (including some grown for edible cottonseed oil) and a smaller percentage of potatoes. Half of all U.S. soybeans are genetically modified as well, mostly to produce a chemical that makes the plants impervious to weed-killing sprays.

So with the exception of explicitly organic food, which flows through independent "identity-preserved" food streams, nearly everything made with soy, corn or cotton in this country ends up containing at least some gene-altered ingredients.

That's a lot of different foods. Soy protein can be found in about 60 percent of all processed food, including frozen meals, baby food, yogurt and other products. And corn, in addition to being the main ingredient in tortilla chips and corn starch, provides the high-fructose sweeteners found in many "natural" sodas, fruit drinks and other products.

U.S. regulators and industry representatives argue that engineered food is, if anything, safer than conventional food. Old-fashioned plant breeding involves the random and uncontrolled reassortment of thousands of genes with every mating, they note. By contrast, biotechnology allows the precise transfer of a single well-understood gene into a plant, leaving little to chance.

Moreover, they say, since 1992 the FDA has required allergy tests like the ones Taylor did for all new food made with genes taken from milk, eggs, wheat, fish, shellfish, legumes or nuts, foods that account for perhaps 90 percent of American food allergies. The agency also insists that gene-altered food be nutritionally equivalent to its conventional counterparts.

Most important, advocates say, the FDA can demand extensive safety testing if the new gene "differs substantially" from those generally found in other food. But critics call that a hollow promise. They note that all 44 crops that so far have gained FDA marketing approval have avoided that scrutiny because the agency has accepted the industry's claims that they are "substantially equivalent" to conventional food.

That is, they claim, because the Food, Drug and Cosmetic Act demands safety testing on all new additives not "generally recognized as safe." Now activists are suing the FDA in federal court to force such testing on the bacterial and other genes being added to food crops.

Safety testing can be difficult, as researchers found with the Flavr Savr tomato, which was given a gene to make it ripen more slowly. When Calgene and Zeneca Plant Science developed that tomato in the early 1990s, no FDA rules were in place. So the companies voluntarily agreed to conduct a full range of tests.

When scientists tried to feed rodents the tomatoes, however, the animals wouldn't eat them, recalled Roger Salquist, one of the scientists involved in creating the Flavr Savr. "I gotta tell you, you can be Chef Boyardee and mice are still not going to like them."

The researchers went so far as to force-feed the tomatoes to rodents through gastric tubes and stomach washes. The procedure made the rodents sick, of course, and revealed nothing about the food's safety. The tomato ultimately won approval from the FDA but failed in the market in part because it was so expensive.

Safety testing is also difficult because there's no widely accepted way to predict a new food's potential to cause an allergy. The FDA is now five years behind in its promise to develop guidelines for doing so. With no formal guidelines in place, it's largely up to the industry to decide whether and how to test for the allergy potential of new food not already on the FDA's "must test" list.

That means there is a small chance that someone will suffer an allergic reaction, and perhaps a serious one, but science can never assure safety with 100 percent certainty, said University of Wisconsin professor Robert Bush, chief of allergies at the Veterans Affairs Hospital in Madison. And when deciding how much effort and expense should be rallied to minimize that risk, Bush said, people should remember that new foods are introduced all the time from other parts of the world without regulators demanding studies on their allergy potential.

"I don't think there was a hue and cry about introducing kiwis onto the U.S. market," Bush said, even though many Americans have proven allergic to them.

The effects of gene-altered crops on the environment are at least as complicated as those on the human body. The EPA requires companies to conduct limited ecological impact tests before marketing gene-altered crops. But while the agency has promised to spell out in detail what crop developers should do to ensure that their gene-altered plants won't damage the environment, it has failed to do so for the past five years.

Meanwhile, several recent scientific studies have highlighted a of potential problems that may be arising from engineered crops.

The most publicized of those was the recent finding that pollen from corn that has been engineered to produce an insecticide called Bt is toxic not only to the caterpillar pest it is aimed at, but also to the monarch butterfly. The laboratory study leaves unresolved whether monarchs are actually being harmed around cornfields. But it inspired a coalition of national environmental groups, including several that had not weighed in on agricultural biotechnology before, to ask the EPA to stop its registration of new varieties of Bt corn until the agency comes up with a more complete ecological safety plan.

At the same time, recent studies have pointed to a variety of other problems that seem to be emerging from Bt corn. One report, for example, suggests that the EPA's primary strategy for preventing the emergence of Bt-resistant insects -- a plan that calls for planting "refuges" of conventional corn in nearby fields -- may be doomed to fail because Bt resistance genes in insects behave differently than scientists had thought.

Another study showed that Bt can alter the time it takes an insect to reach adulthood. That could dash the EPA's hopes that Bt-resistant insects will mate with Bt-susceptible ones and give birth to offspring still vulnerable to the chemical.

Still other studies suggest that Bt corn may be inadvertently killing beneficial insects such as ladybugs and lacewings, which eat insect pests. If true, then the insecticidal crops may be giving reprieves to as many insect pests as they are killing.

And scientists are finding that some engineered crops, such as herbicide-resistant canola in Canada, are cross-pollinating with wild relatives more widely than had been predicted, creating hardy weeds that can survive herbicidal sprays.

Now, the EPA faces a potentially larger problem: whether to approve a new kind of Bt corn called Bt cry9C. It's a decision that many observers see as a test case of just where the agency will draw the line on the degree of risk it is willing to accept.

While other versions of Bt break down harmlessly in the human digestive tract, the cry9C protein remains stable in the human stomach. And because the protein can survive digestion, it has increased potential to cause allergies.

The FDA demands extra allergy testing for new food that contains such stable proteins. And AgrEvo, the German company that is seeking approval for cry9C corn, has conducted some additional tests, including a comparison of cry9C's molecular structure with known allergy-causing proteins. Reassuringly no similarities exist.

But as the agency considers whether to approve the corn for human ingestion, it is up against the reality that there is no surefire way of testing a new protein like cry9C for its potential to cause allergies in people.

"We all wish there was a test where you plug in a protein and out pops a `yes' or `no' answer," said Sue MacIntosh, a protein chemist with AgrEvo.

But there is no such test, short of giving it to a lot of people and seeing what happens.

The EPA is considering the company's application and hopes to make a decision by fall.

THE NEW BIOLOGY

Human cloning, once thought impossible, today seems possible, and perhaps even probable. Growing spare body parts in the lab, once the stuff of science fiction, is being pursued by scientists everywhere. Embryos are being genetically selected to be healthy, or male; "designer babies" may not be too far behind. Plants genetically engineered to produce their own pesticides, and even certain types of plastics, are growing in fields. Science is entering a new world where the once-unthinkable is suddenly doable. The Washington Post is examining this scientific revolution in a series of occasional articles about this new biology exploding at the turn of the century.

ON THE SHELF

Much of the corn, soy and cotton grown in the United States is genetically engineered. Therefore, ingesting food made from genetically engineered crops is almost inevitable.

Percentage of U.S. crop that's genetically engineered:

Corn 33%

Soy 50%

Cotton 50%

Products that may contain one or more genetically engineered ingredient:

Corn

* Juice

* Soda

Cotton

* Nuts

Soy

* Tuna

Corn & Soy

* Frozen pizza

* Spaghetti sauce

* Crackers

* Cookies

* Salad dressing

Corn, Soy & Cotton

* Soup