WASHINGTON (AP) _ Six farmers opposed to genetically engineered crops filed a suit Tuesday alleging that Monsanto Co. and other firms conspired to take over the seed trade and pushed biotech crops to market without adequate environmental and health testing.

The class-action suit, filed in U.S. District Court here, opens a new front in efforts by opponents of genetic engineering to curb the use of biotechnology in agriculture.

Corn and soybeans genetically designed to kill pests or withstand herbicides have become widely popular in the United States, but have met consumer resistance in Europe and Asia. Genetic engineering involves splicing a single gene from one organism to another.

Jeremy Rifkin, a prominent anti-biotech activist who recruited a team of nine law firms to handle the suit, said he wants to ``refocus the global debate'' over genetic engineering to ``corporate abuse of power'' by the companies that developed the crops.

Until now, biotech opponents have focused their efforts on persuading food manufacturers not to buy genetically modified crops and getting governments to require the labeling of altered foods.

The suit alleges that Monsanto, using its biotechnology patents, coordinated with other biotech companies such as DuPont to fix prices and force farmers into using genetically engineered seed.. The lawsuit also alleges there is ``substantial uncertainty'' as to whether the crops are safe.

Five farmers in Indiana and Iowa, including a husband and wife, and one in France are listed as plaintiffs, but the lawsuit was filed on behalf of all farmers who have bought biotech seed. The National Farm Coalition, a left-leaning group opposed to biotechnology, helped develop the suit.

Monsanto officials denounced the lawsuit as a political stunt and predicted it would be thrown out of court.

``This technology has been tested for many years and it's subject to intense regulation. ...We would not put into commerce anything that we're not absolutely confident is safe and effective,'' said Monsanto attorney Dan Snively.

The government estimates that 57 percent of the soybeans grown this year contain a gene that allows it to tolerate use of Monsanto's popular Roundup weed killer. And 30 percent of the corn grown this year was engineered to make it toxic to the European corn borer, a chronic problem for farmers.

The federal government insists that the crops are essentially the same as conventionally bred varieties and pose no threat to humans or the environment.

Advocates say biotechnology has vast potential for developing crops that are more nutritious, need less water and have a variety of new uses, such as bananas that would inoculate children in developing countries against diseases.

For example, a new variety of corn feed under development would cut down on pollution from hog farms by reducing the phosphorus content of manure.

Major farm organizations have been strong defenders of the technology. If anything, Monsanto has been too timid in trying to build public support for the crops, said Nathan Johnson, president of the Minnesota Corn Growers Association.

``I still see them advertising for the farmers' business a lot. If they would put some of that money toward educating the public, we'd be a lot better,'' said Johnson, who says the crops have saved him time and money.

Companion lawsuits are being considered in several foreign countries, including Great Britain and India, said Michael Hausfeld, the lead attorney in the case.