From California's Central Valley to Florida's strawberry fields, tens of thousands of children work in a sea of toxic chemicals whose long-term health effects are almost completely unknown.

In California's onion fields, farm workers, including children, are exposed to methyl parathion, a potent nerve toxin. Among Florida's strawberry fields they encounter captan, a probable human carcinogen. In Midwestern cucumber patches they face endosulfan, a chemical that may cause a host of health problems because of its similarity to human hormones.

Government standards for pesticide residues in the nation's food supply are set with special attention to the children who eat that food. Yet those standards intentionally ignore a more vulnerable class of children -- working kids who help harvest America's food.

Those who work in the fields receive pesticide doses many times higher than the law allows in American diets. It's difficult to say exactly how much higher, because the research needed to find out simply hasn't been done.

"Everybody stands there with a straight face and talks about protecting children, and they don't do anything to protect child workers,'' said Marion Moses, a pediatrician with the Pesticide Education Center in San Francisco. "I don't think that we should be dosing children very early in life with toxic chemicals.''

Yet we do.

An unreleased U.S. Department of Labor survey shows that 123,000 children between the ages of 14 and 17 work in America's fields. Uncounted thousands more are under 14.

Associated Press reporters who visited farms over the last five months found working children as young as 4. Mothers who can't afford day care carry infants into the fields. Two years ago, a 14-year-old girl gave birth in a New Jersey berry patch.

In Ohio this summer, 6-year-old Ramiro Silva and his sister picked pesticide-dusted cucumbers and ate them unwashed for lunch. Alejandra Renteria, also 6, sometimes refused to wear rubber gloves because they were too big and clumsy for her.

"My arms get itchy sometimes, but I like to work,'' Ramiro said. Itchy irritations are common in pesticide exposure.

"Think of yourself in your own teen-age and pre-teen-age years, and think of the kamikaze-pilot things that you did. These children are no different,'' said Vincent Garry, director of environmental medicine and pathology at the University of Minnesota.

"Protecting the health of our children is one of our highest priorities,'' Environmental Protection Agency administrator Carol Browner told a conference of doctors and scientists in September.

But until this year, the federal government spent next to nothing for occupational health and safety research on child farm workers. The National Institute of Occupational Safety and Health did hand out $2.5 million for research on injuries to child farm workers, but the effort pales next to the $700 million the U.S. Department of Agriculture's Agricultural Research Service spends each year on crop and livestock studies.

Many farm workers believe pesticides make them and their children sick. In Salinas, Calif., Jesus Lopez wonders why so many farm workers in the area get sick every summer. Just about the time the fields are plowed for the year's second crop, people develop nausea, coughing and muscle aches.

"The doctors always say it's a flu,'' said Lopez, a community worker for California Rural Legal Assistance. ``But it's very curious to me. Why, every single year in June and July, do we get the flu?''

Flulike symptoms are a classic sign of pesticide poisoning. Children on farms occasionally suffer severe pesticide poisoning, sometimes fatally.

Late in the afternoon of April 1, 1990, a 3-year-old girl playing in front of her trailer home in California's San Joaquin Valley suddenly lost control of her body and began foaming at the mouth. By the time the girl arrived at the local emergency room, she was near death. She recovered eventually.

A report filed with the California Department of Pesticide Regulation concluded the child had been poisoned by aldicarb, a highly toxic insecticide that works the same way on people as it does on bugs -- like nerve gas.

"Somebody had parked a tractor with pesticide material on it right in front of the play area,'' said Michael O'Malley, the author of the report and a physician at the University of California, Davis.

Such confirmed incidents of acute pesticide poisoning are rare -- or at least rarely reported. Of greater concern to experts is long-term, low-level damage that can show up decades after a child has picked his or her last berry.

"Compared to late-in-life exposures, exposures to pesticides early in life can lead to a greater risk of chronic effects that are expressed only after long latency periods have elapsed,'' a National Academy of Sciences committee said in a 1993 report.

The report focused on pesticides in children's diets. It cited a number of reasons to believe that youngsters are especially sensitive to toxic chemicals. A child's rapid growth can be disrupted or interrupted by chemicals. They suffer the ill effects of some pesticides at lower doses than adults do, and because their metabolisms are faster they tend to process toxins faster than adults. They also have a lot more years left to develop cancer and other long-term health problems.

"It's just not a good idea to be exposing rapidly growing cells or organs to compounds that we know produce a carcinogenic effect in mammals,'' said John Wargo, a professor of environmental studies at Yale University.

A few dozen studies have looked at the rates of cancer and birth defects among children whose parents work with pesticides or use them at home. The results are worrisome.

In Denver homes where pesticides were used, children were more likely to develop leukemia, brain tumors, lymphoma and soft-tissue sarcomas, a study of nearly 500 kids found. Another study of 178 children in the United States and Canada found that leukemia was 11 times more common in children under five if their parents worked with pesticides.

"The implication is that children must be a particularly susceptible group,'' said Shelia Hoar Zahm of the National Cancer Institute.

That's why the Food Quality Protection Act of 1996 requires the Environmental Protection Agency to consider children, who are most vulnerable to such health effects, when it sets limits for pesticides in food.

The law is so strict that even the environmentalists who lobbied for it can hardly believe it passed the 104th Congress unanimously. But the Food Quality Protection Act specifically forbids the EPA from considering occupational exposures, which are known to be much higher than those generally found in food and water. The act goes out of its way to exclude the children and adults who pick America's produce.

"It's an explicit, purposeful exception,'' said Ralph Lightstone of California Rural Legal Assistance. "They carved farm workers out.''

House Commerce Committee staffer Kay Holkgum, who helped write the food quality law, argues that farm workers are protected under other laws geared toward occupational health. For example, there are laws that require posting of notices about pesticide spraying, and that specify how soon after spraying workers can return to the fields.

But nobody denies that farm workers, both adults and children, are exposed to much higher pesticide levels than the general public.

In Washington state's apple orchards, for example, workers have 16 times the pesticide-breakdown products in their urine than their neighbors who don't work in agriculture.

The food quality law will give farm workers an indirect measure of protection, however, and that's the silver lining in this cloud, said Richard Wiles of the Environmental Working Group, a Washington, D.C. environmental advocacy group. Farms will be forced to reduce pesticide use somewhat in order to meet the stricter EPA tolerances for pesticides in food.

But it would have been better for the children in the fields, said San Francisco pediatrician Moses, if farm-worker rather than consumer safety were the focus of America's strongest pesticide law.

"You protect the worker in the workplace, I guarantee you protect the consumer in the marketplace,'' Moses said. ``The other way around doesn't work.''