LA CONNER, WASH. -- A small noisy tractor chugged the length of Kirby Johnson's pea field, its outstretched sprayers laying atop the earth a thick low cloud of a yellow as bright as sunflowers. Yellow streaked the tractor tires, yellow dusted the windows of its cab, and when the engine quieted and Johnson stepped down from the back, the hand he extended in greeting was yellowed nearly to the wrist.

There was yellow across the leg of his zip-up protective suit, too, and Johnson looked amused as he unzipped. "Since I was a sophomore in high school, which unfortunately was 30 years ago, I've sprayed this field every year without a cab -- without any protection at all," he said. "I am a far better sprayer without this cab. When you're in there with your windows and your ear muffs, you're oblivious to anything."

The stained coveralls and grudgingly installed tractor cab of Kirby Johnson are part of the residue of a coast-to-coast battle that suggests by its very proportions some of the difficulty of modern American pesticide regulation.

The bright yellow comes from a chemical called dinoseb, and since it began last autumn, the dinoseb conflict has set the Environmental Protection Agency against the federal courts, drawn interest and legal briefs from environmental and labor groups and threatened to stick the EPA next year with a bill estimated at $60 million to $120 million -- the high end of which is, by some estimates, nearly twice the agency's entire annual pesticides budget.

The target of all this heat is a popular and inexpensive weedkiller that is all that stands, Johnson and his twin brother Curtis insist, between them and 285 acres of weeds where their peas are supposed to grow. Smartweed, mustard, henbit and lamb's-quarters -- all the tiny green shoots that, left unchecked, would soar to take sun and nutrients from the growing peas. And all the shoots -- every one of them, the Johnsons pronounced as they stepped through the newly sprayed peas -- would be dead by late afternoon.

"Like burning them with a flame," Kirby Johnson said.

The problem, according to reports examined recently by pesticide experts at the Environmental Protection Agency, is that dinoseb is dangerous -- so dangerous, EPA Administrator Lee M. Thomas declared last fall, that it must be banned immediately. On Oct. 7, in only the third emergency pesticide suspension in EPA history, Thomas declared that because dinoseb had been linked to birth defects, cataracts, sterility and poisoning of agricultural workers, further use of the chemical would constitute an "imminent hazard" to the environment and human health.

If an outsider wanted a crash course in the complexities of pesticide regulation, this might be an instructive place to start -- with an emergency suspension of a chemical that farmers like the 46-year-old Johnson twins have been using since they were old enough to drive a tractor. Thomas cited numerous studies in his Oct. 7 dinoseb ban, but most alarming were new reports showing birth defects in dinoseb-exposed rabbits and rats.

The testing was done as part of an ongoing EPA effort to update labels and testing on the hundreds of registered pesticides now in use. The process, laborious and often criticized by environmental activists for its plodding pace, is aimed at pesticides approved in days of less rigorous standards. "It's sort of a rule of thumb that if a test was done before 1970, it's probably no good, in terms of scientific acceptability," said Edward Gray, EPA assistant general counsel.

Last year, the dinoseb rabbit and rat study results arrived at the EPA. Each study was conducted by a separate company, but both, said EPA project review manager Michael McDavit, "pointed the same direction." What they suggested to EPA scientists, according to Thomas' suspension order, was that animal birth defects were being caused by doses lower than what some farmworkers were receiving -- and that a pregnant woman might irreversibly damage her fetus through just one exposure to dinoseb.

Farmers and workers using dinoseb were so greatly at risk, the suspension order said, that even protective clothing and closed tractor cabs would not provide enough protection. "No adequate means exist to warn or prohibit pregnant females from being in the proximity of farms that use dinoseb," Thomas wrote. "Women could contact contaminated surfaces on the farm premises, or handle contaminated clothing or protective equipment."

Growers reacted swiftly to the ban. The EPA estimates that farmers annually use between 7 million and 11 million pounds of dinoseb on a wide variety of crops, including soybeans and peanuts; pulling the chemical, by the agency's calculations, would cost growers $80 million to $90 million a year.

"It'd be like telling the medical profession, 'Hey, we're going to jerk penicillin,' " Curtis Johnson said.

Northwestern farmers in particular pleaded impending financial disaster, saying the local climate made dinoseb alternatives minimally effective. Last March, Thomas approved a partial exception. In Washington and Idaho, he ordered, growers of dry peas, lentils and chickpeas could kill their weeds with dinoseb if they followed certain safety restrictions.

The restrictions themselves were controversial; they required protective measures, such as closed tractor cabs, which Thomas had earlier called inadequate. They also galled labor and women's groups with a provision that dinoseb work was forbidden to any woman "of child-bearing age, i.e., under the age of 45."

And only the dry pea, lentil and chickpea farmers could use it. "Right away, my first thought is, 'Loophole,' " Curtis Johnson said. "If those guys can spray it over there and it doesn't make them sterile, then hey, we can spray it over here."

Green pea growers took the EPA to court, joined by other northwestern growers who argued that they were facing a potential $39 million crop loss and that the EPA had been arbitrary in approving such limited dinoseb use. A U.S. District Court judge in Oregon upheld the growers' group, giving the Johnson brothers and some of their northwestern colleagues a last-minute reprieve to use dinoseb on this summer's crops.

But they have to follow the new safety rules. No women under 45 may work with them. Farmers elsewhere in America -- including the Southeast, where the EPA estimated that the dinoseb ban would mean an annual $71 million loss to peanut farmers alone -- are still prohibited from using the chemical.

The EPA is appealing the Oregon decision and simultaneously proceeding with its plans to hold hearings this summer on permanent cancellation of dinoseb. EPA dinoseb experts have handled petitions from growers in Maryland, Delaware, Virginia and Pennsylvania, all of whom have claimed serious economic hardship without the chemical.

Even if the anti-dinoseb forces prevail, hurdles remain. Banning dinoseb permanently will be an expensive proposition -- expensive enough, some officials have suggested, to threaten EPA's entire pesticides regulation budget.

The bite comes out of a single subsection of the federal law that regulates pesticides. When the law was rewritten in 1972, it included a guarantee that the EPA would purchase, at a price up to "fair market value," any outstanding stock of a chemical banned by the agency. If the agency prohibits permanently any use of dinoseb, it must buy and then offer to dispose of every last ounce of the chemical, whether it is stacked in Uniroyal warehouses or stored in Curtis Johnson's shed.

The process is referred to as "indemnification," and it has cost the EPA money before -- EDB and 2,4,5,T- Sylvex are among chemicals the EPA has banned and bought up. But if the cost of every indemnification over the last 15 years was added together, the total would be less than half the anticipated tab for the purchase and destruction of dinoseb.

The money, as the law is now written, apparently would come from the EPA's pesticides program budget, about $70 million this year. "We're sitting around trying to figure out what happens when we start getting claims for dinoseb," Gray said. "They've been talking about anywhere between $60 {million} and $120 million for disposal and indemnification."

There is precedent for pulling indemnification money from other budgets; the EPA has been able to obtain congressional appropriations or dip into Justice Department funds. But EPA pesticide officials, who don't like the concept of indemnification, say no arrangement has been made to pay the heavy costs for dinoseb cancellation.

"That money right now would appear to come straight out of the pesticide program's budget, and the low end is equal to our entire pesticide money," said Jim Lamb, special assistant to EPA pesticides head John Moore. "We very much would like indemnification to be repealed. We don't believe the federal government should be the insurer of the pesticide industry."

Chemical manufacturers say indemnification is only fair, since chemicals such as dinoseb were registered long ago by a government that now proposes, as National Agricultural Chemicals Association spokesman Luther Shaw said, to change the rules. "We think the government has some obligation in that kind of a situation," Shaw said.

But environmental activists say they can see no parallel anywhere in government for the massive taxpayer-funded purchase of a privately manufactured product found to be a serious health hazard. And the specter of indemnification costs, they insist, sets up a major disincentive to pulling dangerous chemicals off the market.

Some environmentalists have lobbied for a ban on alachlor, a cancer-linked pesticide that EPA officials say is not dangerous enough to warrant suspension. If alachlor were to be banned, indemnification costs would total $323 million, according to one estimate recently presented in testimony to a Senate Appropriations subcommittee. Disposal costs could double that figure.

"You can imagine the chilling effect that has on the agency to ever go back on a chemical," said Al Meyerhoff, attorney for the Natural Resources Defense Council. "It's an outrage. It makes the taxpayer liable for a defective product. You put an automobile on the market and the steering wheel breaks -- the government has to buy every Corvair on the market?"

Meyerhoff, joined by attorneys for the American Civil Liberties Union and the AFL-CIO, has moved to join EPA's fight with the Oregon court. Having lost an earlier battle to keep the Northwest farmers from spraying for this growing season, Meyerhoff said he is unconvinced by warnings of financial ruin among farmers barred from using dinoseb.

"We concede that yields might go down," Meyerhoff said. "How many pounds of lentils is a deformed baby worth? Where would you tolerate that in any other context? We have a right to run a law office here and expose our employes daily to a hazardous, birth defect-causing chemical because we want to practice law? It's ludicrous."

When that argument was set before the Johnson brothers, each resting his elbows on the round deck table between Curtis Johnson's house and the newly sprayed pea field, Kirby Johnson sighed and extended two yellow-stained palms. "I have never used gloves until this year," he said.

As teen-agers, the Johnsons said, they spent two or three months a year yellowed nearly to the elbows. They sprayed dinoseb from open tractors, turned their faces when they began to choke, washed it out of their hair at night. Their children are healthy, they said; their wives have had no miscarriages, and all their lives, the local cats and dogs have bred normal-looking litters on dinoseb-sprayed fields.

"If it's so dangerous, why aren't we hurting from it?" Curtis Johnson demanded. "Every time I go into a smoke-filled room, I think about dying from lung cancer, too. But it doesn't mean I can go into my favorite bar and enjoy a smoke-free evening."

Rabbits and rats, the Johnson brothers said, are not human beings. And it is true, as the Johnson brothers observe, that there are no human studies of dinoseb's effect on babies and reproductive systems. There has been little study examining the relationship between any pesticide and reproductive problems, and that is partly because of the difficulty of studying farmworkers, many of whom are migrants.

"Clients don't come in knowing what they've been sprayed with, or what the problem is," said Michelle Mentzer, an attorney for Evergreen Legal Services, which counsels farmworkers in the central Washington town of Granger. "All they know is, they've had an accident with quimico" -- chemical.

The workers are often mobile, unable to speak English and uneasy about seeking medical treatment, Mentzer said. They often are given minimal protective clothing, if it is offered at all. Those who develop ailments may be living in another state by the time the ailments appear, and there is no state-to-state registry that would help tally reproductive problems. A new California birth-defects registry, which just expanded its study area to the agricultural counties of the state's central valley, is apparently the first effort in the nation to monitor birth defects across a broad population.

"The bottom line is, nobody has looked," said John Harris, the pediatrician and epidemiologist who heads the monitoring program.

The Johnson brothers, who said their family farms their 515 acres without outside labor, are uneasy about what will happen to their crops if dinoseb is permanently banned. They often drive up the road to the plot where their neighbor is testing one of the chemicals proposed as an alternative, and they are watching the weeds there growing among the peas.

Early this spring, when they had their dinoseb but were told for a while that they could not use it, the Johnson brothers contemplated dying it purple so no one would know what they were spraying. "It's a difference between surviving economically or not," Curtis Johnson said. "We're a little too old for civil disobedience, but it worked pretty well in the '60s."

Did none of the warnings scare them?

"You chose to be a farmer," Kirby Johnson said. "People are losing arms and legs in tractors every day . . . . It's a high-risk deal."

Kirby Johnson thought for a while, then said that almost every death in their family had been from cancer.

"Hell, maybe that's dinoseb," Curtis Johnson said. "I don't know."

"But it doesn't dissuade me," Kirby Johnson said.