ST. LOUIS -- Opponents of the proposed Holcim cement plant in Ste. Genevieve County have asked two federal agencies to halt the $600 million project, saying it would destroy wetlands and pollute air and water.

Eight national and regional environmental groups registered their opposition Friday in a letter to the U.S. Environmental Protection Agency and the U.S. Fish and Wildlife Service.

They asked the agencies to do everything they can to halt the project. The Swiss-based company wants to build the nation's largest cement plant along the Mississippi River.

The letter asks the two federal agencies to intervene through the Army Corps of Engineers wetlands permit process. Once the corps issues the permit -- which could happen by the end of the year -- the agencies can request formal review by their top officials. The EPA also can veto a wetlands permit.

Mike Mullin, the head of Holcim's government affairs division, said the letter was disappointing.

He said the project has been studied extensively and revised with the goal of minimal environmental impacts, while bringing hundreds of jobs.

Groups signing the letter include American Rivers, Environmental Defense, the Natural Resources Defense Council and the Sierra Club.

EPA officials were not available for comment.

The plant, which company officials said could start production within three years, would be located about 40 miles south of St. Louis, and produce 4.4 million tons of cement a year.