As the crucial fall harvest season approaches, many U.S. farmers and other agricultural workers are in a near panic because of escalating uncertainty over genetically engineered crops.

Farmers planted millions of acres of the high-tech crops this year. But foreign buyers are rejecting them in droves, despite aggressive U.S. marketing efforts and assurances of their safety.

In the past month alone, Japan's two biggest breweries and a major Mexican corn tortilla maker said they would no longer use U.S. gene-altered corn in their products, adding to troubles caused by the European Union's previous large-scale rejection of such crops.

Even Iams Co., the Ohio-based pet food maker, recently told its grain suppliers it would no longer accept genetically engineered corn for use in its premium dog and cat chows unless the corn varieties were among the few approved by the European Union.

Twelve days ago those developments hit home for many farmers, when Archer Daniels Midland (ADM), the big Illinois-based buyer and exporter of farm commodities, made the ominous recommendation that U.S. farmers segregate their gene-altered and non-altered crops at harvest because of heightened demand for conventional varieties both domestically and abroad.

The announcement left many farmers feeling angry and betrayed.

"American farmers planted [gene-altered crops] in good faith, with the belief that the product is safe and that they would be rewarded for their efforts," the American Corn Growers Association said in a statement last week. "Instead they find themselves misled by multinational seed and chemical companies and other commodity associations who only encouraged them to plant increased acres of [these crops] without any warning to farmers of the dangers associated with planting a crop that didn't have consumer acceptance."

More than 40 genetically modified crops have been given the green light by U.S. regulators as safe to eat and environmentally friendly. And most farmers express satisfaction with the varieties. The crops contain genes from bacteria and viruses to make them resistant to insects and weed killers, promising farmers a better deal.

Agricultural biotechnology companies promoted the gene-altered varieties heavily during the past two years, and farmers planted them in record numbers this year. But a wave of consumer distrust that started in England two years ago has swept around the globe and in recent months has shown signs of taking hold in the United States -- especially since the widely reported discovery this summer that pollen from corn engineered to produce an insecticide could kill Monarch butterflies.

The result has been an unexpected twist: Many farmers who did not plant the new varieties are resting easier than their progressive counterparts because much of the world is clamoring for their ordinary harvest. Some of these farmers are even being promised they'll be paid a premium for their old-fashioned corn and soybeans.

The reverse economics, in which farmers who paid premium prices for high-tech seeds are being shunned and may have to sell their harvest at a discount, is cultivating a high level of frustration.

"I've been in this business for 30 years and this indecision about genetically engineered seeds and what the future holds for farmers is the worst I've seen," said Chuck Simmons, president of Bio-Plant Research in Camp Point, Ill., a marketer of gene-altered soy and other seeds. "This is the Y2K of agriculture."

Until recently, the debate over gene-altered food had its impact almost entirely on Washington agencies and big-city corporate offices. Under pressure from foreign buyers, for example, Secretary of Agriculture Dan Glickman this summer called for an independent assessment of whether the U.S. biotech crop approval process is adequate. The National Academy of Sciences is preparing a report on the environmental implications of the new crops. And the American Medical Association said last week it would revisit and rewrite its nine-year-old unflinchingly positive policy statement on the safety of biotech foods.

This summer, however, the issue started to affect biotechnology companies directly. Sales abroad came to a near halt. And mimicking the protests that last year paralyzed biotech agriculture in Europe, U.S. activists started uprooting fields of gene-altered plants during midnight raids on company test plots in California, Maine and Minnesota. In the latest raid, protesters in Vermont planted placards with pictures of Monarch butterflies in a field of engineered corn they had ruined.

But it was the announcement from Archer Daniels Midland that really brought the debate home to the American farmer.

"Some of our customers are requesting and making their purchases based upon the genetic origin of the crops used to manufacture their products," the statement said. "If we are unable to satisfy their requests, they do have alternative sources for their ingredients. We encourage you as our supplier to segregate non-genetically enhanced crops to preserve their identity."

The most immediate problem raised by the new announcement is how to accomplish that segregation. More than half of the nation's soybeans and about a third of this summer's corn were genetically engineered. But many of the grain elevators and other storage depots that farmers bring their harvests to don't have multiple bins or the capacity needed to keep engineered and non-engineered varieties apart, said Randy Sexton, of Niantic Farmers Grain Co. in Niantic, Ill.

"We do 75 percent of our volume within 30 days after harvest," Sexton said. "We unload one truck right after another, and we're not well suited to switch from one load to another."

Moreover, Sexton said, elevator operators would have to clean their equipment between batches to prevent any carryover of engineered varieties into conventional ones -- a difficult job that would cost the company time and wages. And what if some contamination occurred? Who would be responsible?

"We hire temporary helpers and farmers hire temporary drivers and it would be very easy to get a truck mixed up," Sexton said. "And if you contaminate ADM's supply, there's a potential for liability."

For farmers too, segregation is a problem. If their local elevator decides to take only one kind of crop or the other, because of an inability to keep them separate, farmers may have to drive many miles farther than before to unload their harvest, again costing time and money.

With farmers facing record low commodity prices, and grain elevator operators also working on very narrow profit margins, both groups are asking who will pay for the added expenses of segregation.

"Growers are not in any position to absorb that cost," said Gary Bradley, a spokesman for the National Corn Growers Association.

In deciding what seed to buy next year farmers will rely on a calculation of how much the engineered seeds cost relative to conventional seeds, how much money they may save if the new seeds keep their promise of higher yields and lower pesticide costs, and how much they may lose next fall if engineered crops sell for less than conventional ones.

Some agricultural economists wonder whether farmers will retreat to conventional seeds, thus saving them the trouble of having to segregate and possibly buying themselves a premium next fall.

Gary Goldberg, chief executive officer of the American Corn Growers Association, said initial projections for next year's planting of engineered corn called for an increase of about 20 percent or more over this year's acreage. "We now think there may be a 20 to 25 percent reduction in [engineered] acres next year because of this uncertainty issue."

Seed suppliers say demand may not increase as it has, but they also don't expect a big downturn."We have genetically enhanced seeds as well as traditional varieties and we will continue to supply growers with whatever they want and need," said Lori Fisher, a spokeswoman for Monsanto in St. Louis. "We do expect to see a growth in bags of genetically enhanced seeds sold. We believe farmers will continue to adopt the technology."