WASHINGTON -- You may not want to eat genetically engineered foods. Chances are, you are eating them anyway.

Genetically modified plants grown from seeds engineered in labs now provide much of the food we eat. Most corn, soybean and cotton crops grown in the United States have been genetically modified to resist pesticides or insects, and corn and soy are common food ingredients.

The Agriculture Department has approved three more genetically engineered crops in the past month, and the Food and Drug Administration could approve fast-growing genetically modified salmon for human consumption this year.

Agribusiness and the seed companies say their products help boost crop production, lower prices at the grocery store and feed the world, particularly in developing countries.

The FDA and USDA say the engineered foods they have approved are safe -- so safe, they don't even need to be labeled as such -- and can't be significantly distinguished from conventional varieties.

Organic food companies, chefs and consumer groups have stepped up their efforts, so far unsuccessfully, to get the government to exercise more oversight of engineered foods, arguing that the seeds are floating from field to field and contaminating pure crops.

The groups have been bolstered by a growing network of consumers who are wary of processed and modified foods.

Many of these opponents acknowledge that there isn't much solid evidence showing that genetically modified foods are somehow dangerous or unhealthy.

It just doesn't seem right, they say. For them, it's an ethical issue.

"If you mess with nature there's a side-effect somewhere," said George Siemon, CEO of Organic Valley, the nation's largest organic farming cooperative, which had more than $600 million in sales last year.

"There is a growing awareness that our system makes us all guinea pigs of sorts," he said.

The U.S. government has insisted that there is not enough difference between the genetically modified seeds its agencies have approved and natural seeds to cause concern.

But Agriculture Secretary Tom Vilsack, more so than his predecessors in previous administrations, has acknowledged the debate over the issue and a growing chorus of consumers concerned about what they are eating.

"The rapid adoption of GE crops has clashed with the rapid expansion of demand for organic and other non-GE products," Vilsack said in December as he considered whether to approve genetically modified alfalfa.

"This clash led to litigation and uncertainty. ... Surely there is a better way, a solution that acknowledges agriculture's complexity, while celebrating and promoting its diversity."

Vilsack later approved the engineered alfalfa for use, along with sugar beets and a type of corn used in ethanol, to the disappointment of the organic industry, but he said the department would do additional research on ways to prevent contamination of natural seeds and improve detection of contamination.

Organic companies have praised Vilsack for even acknowledging the issue, as large seed companies such as Monsanto, and the substantial chunk of agribusiness that use their seeds, have long held sway at USDA.

The organic industry has a lot to lose. USDA regulations do not allow genetically modified seeds to be used in organic production, and organic farmers say that as engineered crops become more common, it will be harder to prevent contamination.

The industry also is concerned that fears of contamination could hurt its sales, especially in Europe, where consumers have been extremely hesitant about biotech foods.

While opponents of engineered foods haven't found federal agencies overly receptive to their concerns, they have been able to delay some USDA approvals with lawsuits.

The alfalfa decision followed a lengthy court battle that was closely watched not only by the organic industry, but by consumers, a development that opponents believe will help their cause.

"We're seeing a level of reaction that is unprecedented," said Jeffrey Smith, an activist who has fought the expansion of genetically engineered foods since they were first introduced 15 years ago, and has written two books on the subject.

"I personally think we are going to hit the tipping point of consumer rejection very soon," he said.