By Carey Gillam

(Reuters) - A coalition of more than 2,000 U.S. farmers and food companies said Wednesday it is taking legal action to force government regulators to analyze potential problems with proposed biotech crops and the weed-killing chemicals to be sprayed over them.

"These are the most dangerous chemicals out there," said John Bode, a Washington lawyer and lobbyist hired by the Save Our Crops Coalition.

Unlike past protests of new biotech crops, the coalition comprises many grower groups that use and support biotechnology. This is not a biotech complaint, they say, but one focused on the danger of the chemicals to be used with the biocrops.

Global chemical and seed companies including Dow AgroSciences, a unit of Dow Chemical, and Monsanto Co. are racing to roll out combinations of genetically altered crops and new herbicides to counter spreading weeds that are choking millions of acres of U.S. farmland.

"They (farmers) need this new technology," said Joe Vertin, global business leader for Dow's new herbicide-protected crops called "Enlist."

Dow and Monsanto say the new herbicide combinations and crops that tolerate those chemicals are badly needed by corn, soybean and cotton farmers as weeds increasingly resist treatments of the most commonly used herbicide, glyphosate-based Roundup.

Critics says key ingredients in the new herbicides -- 2,4-D for Dow and dicamba for Monsanto -- are already in use in the marketplace and have proved hard to track. Wind, heat and humidity can move the chemical particles miles, damaging gardens, crops and trees, they say.

"The danger that 2,4-D and dicamba pose is a real threat to crops...nearly every food crop," said Steve Smith, director of agriculture at Red Gold, the world's largest canned tomato processor, and a leader of the Save Our Crops Coalition.

The coalition represents more than 2,000 farmers and groups such as the Indiana Vegetable Growers Association, the Ohio Produce Growers and Marketers Association, and major food processors Seneca and Red Gold.

Over the last four years, more than $1 million in damages have been filed in lawsuits and insurance claims by Midwestern growers who have suffered crop losses due to 2,4-D and dicamba that has drifted onto their farms, Smith said.

Those losses would increase with the new herbicide-tolerant crops because farmers would then be spraying more of the herbicides and later in the growing season, the coalition says.

In their legal petitions, the group is asking the Department of Agriculture (USDA) to conduct an environmental impact study on the ramifications of a release of a new 2,4-D tolerant corn that is to be accompanied by Dow's new herbicide mix containing both 2,4-D and glyphosate. It wants a similar environmental impact statement on the dicamba and glyphosate herbicide tolerant crops being developed by Monsanto.

The coalition is also demanding the Environmental Protection Agency (EPA) conduct a Scientific Advisory Panel (SAP) meeting and appoint advisors to the panel to address herbicide spray drift.

Dow plans to roll out as early as 2013 its 2,4-D tolerant corn and new 2,4-D based herbicide. The 2,4-D ingredient was a component of Agent Orange defoliant used in Vietnam.

A petition started by the Center for Food Safety says 2,4-D will "likely harm people and their children, including farmers, and the environment," and that USDA has not properly assessed the impact of Dow's plan for a new 2,4-D based crop system.

Dow AgroSciences executives say the fears are unwarranted as their herbicide formulation does not have the problematic "drift" problems that other 2,4-D formulations have.

"We're highly into stewardship and want to be sure the farmers get this right," said Dow spokeswoman Kenda Resler-Friend. "Nobody wants trouble with their neighbor. They want to do the right thing."

(Editing by Ryan Woo)