KANSAS CITY, Mo., March 29 (Reuters Legal) - A consortium of U.S. organic farmers and seed dealers filed suit against global seed giant Monsanto Co. on Tuesday, in a move to protect themselves from what they see as a growing threat in the company's arsenal of genetically modified crops.

The Public Patent Foundation (PUBPAT) filed the suit on behalf of more than 50 organizations challenging the chemical giant's patents on its genetically modified seeds. The group is seeking a ruling that would prohibit Monsanto from suing the farmers or dealers if their organic seed becomes contaminated with Monsanto's patented biotech seed germplasm.

Monsanto is known for its zealous defense of its patents on a range of genetically altered crops. Its patented "Roundup Ready" soybeans, corn and cotton are favorites of U.S. farmers because of their ability to withstand herbicide treatments.

Monsanto called the lawsuit misleading and a "publicity stunt" and said it has never sued and has committed to never suing farmers over the inadvertent presence of biotechnology traits in their fields.

Legal precedent supports the validity of Monsanto patents, the company said.

"These efforts seek to reduce private and public investment in the development of new higher-yielding seed technologies. While we respect the views of organic farmers as it relates to the products they choose to grow, we don't believe that American agriculture faces an all-or-nothing approach," Monsanto said in a statement.

Monsanto has filed scores of lawsuits and won judgments against farmers they claimed made use of their seed without paying required royalties. Many farmers have claimed that their fields were inadvertently contaminated without their knowledge, and the issue has been a topic of concern for not only farmers, but also companies that clean and handle seed.

"This case asks whether Monsanto has the right to sue organic farmers for patent infringement if Monsanto's genetically modified seed should land on their property," said Dan Ravicher, executive director of PUBPAT, a nonprofit legal services organization, which filed the suit in New York.

The suit also alleges that Monsanto's GMO seeds do more harm than good and claims the patents on genetically modified seed are invalid because they don't meet the "usefulness" requirement of patent law.

"Some say genetically modified seed can coexist with organic seed, but history tells us that's not possible," said Ravicher. "It's actually in Monsanto's financial interest to eliminate organic seed so that they can have a total monopoly over our food supply."

The suit asks the court to declare that an inadvertant mixing of Monsanto seeds with those of a farmer who does not wish to use them amounts to a trespass on the part of Monsanto.

"As nontransgenic seed farmers and seed sellers, Plaintiffs already have to deal with the constant threat of transgenic seed contamination that could destroy their chosen livelihood. They should not also have to live with the threat of being sued for patent infringement should that travesty come to pass," the lawsuit states.

Monsanto's genetically altered seeds have been a market mainstay since the mid-1990s, and many of its rivals have their own brands of biotech crops that tolerate herbicide, resist insects and have other useful qualities engineered into them.

The case is: Organic Seed Growers and Trade Association et al v. Monsanto Company and Monstanto Technology LLC, U.S. District Court for the Southern District of New York, No. 11-cv-2163.

For the plaintiff farmers: Daniel Ravicher and Sabrina Hassan of The Public Patent Foundation (Cardozo School of Law)

For Monsanto: Not immediately available.

(Reporting by Carey Gillam of Reuters; Additional reporting by Jeff Roberts of Reuters Legal)