he Agriculture Department is allowing widespread planting of genetically modified alfalfa, attempting to bring to a close a lengthy legal and regulatory process in which organic producers attempted to curtail the use of the modified crop.

The decision announced Thursday is a blow to the organic foods industry, which complains that modified seeds can contaminate their organic crops through pollination, bringing genetically modified foods into their fields. The Agriculture Department has said the modified alfalfa — used primarily for hay for cattle — is safe, but some consumers don't want to eat foods derived from it, including milk or beef. The growing organic industry and its millions of consumers have long been wary of genetically modified seed companies such as Monsanto, citing the purity of natural seeds, the ethics of eating modified foods and possible environmental damage from creating new varieties of crops.

Farmers who use the seeds say they boost their crop yields and help reduce prices for consumers in the grocery store. The biotech companies say they are doing their part voluntarily to restrict where their alfalfa crops are planted so they don't contaminate other, non-engineered crops.

Agriculture Secretary Tom Vilsack had said in December that the department was considering, as one of several options, government restrictions on planting of the modified alfalfa, giving producers of organic and other non-engineered alfalfa hope. But the department came under sharp criticism for that proposal from the genetically engineered-seed companies and Congress.

In a hearing last week, several members from farm states questioned the proposal, saying it politicized the regulatory process. Because the alfalfa is safe, its planting should be allowed, they argued.

Vilsack disagreed that the issue had been politicized, saying the department is simply trying to help two large agricultural industries — organics and biotech companies — peacefully coexist. He said Thursday the department will make other efforts to ensure that organic and other non-modified alfalfa seeds remain pure by doing additional research on preventing cross contamination of seeds and improving detection of that contamination. He said the department will make efforts to ensure that pure varieties of the alfalfa seeds are preserved.

The organic industry said it wasn't enough.

"Consumers will not tolerate the accidental presence of genetic engineered materials in organic products, yet GE crops continue to proliferate unchecked," said Christine Bushway, director and CEO of the Organic Trade Association.

George Siemon, CEO of Organic Valley, one of the country's largest organic food companies, worked with the USDA as it made the decision. He said the controversy over the alfalfa has swirled as organics have grown exponentially and biotech crops have prospered as well. A large number of crops — including soybeans and corn — are made from some sort of genetically engineered component.

"Organics have succeeded and also the biotechnology sector has succeeded, and it's naturally coming to a head right now," he said. "There's no doubt that in the last five years, right or wrong, consumer concerns about this technology has just magnified."

USDA's decision on the alfalfa — which is genetically engineered to be resistant to the popular weed killer Roundup, so it can be used without hurting the crop — has wound through the regulatory process and the courts. A 2007 federal court decision said the USDA had not given enough consideration to the effects of the modified alfalfa, and a judge placed an injunction on planting the crop. The U.S. Supreme Court said last year that decision had gone too far.