As the United States increasingly looks to develop alternative forms of energy, solar companies that want to build huge power plants have honed in on vast tracts of open space in the Mojave Desert, which cuts across California, western Arizona, and parts of Nevada and Utah.

Already, the Bureau of Land Management has received more than 210 applications, covering more than 2.1 million acres of land, from such companies. In Arizona, there are 34 applications, involving more than 682,000 acres.

Ironically, the rush to build "green energy" is dividing environmental groups, many of whom believe such projects will irreparably harm ecologically sensitive habitat.

The Mojave, for example, is home to the endangered desert tortoise, among other species.

If millions of acres are razed for solar plants, swaths of wildlife habitat will be eliminated, putting the desert tortoise, the Mojave ground squirrel and the American badger at even greater risk, conservationists say.

"I agree that we need to be making a rapid and dramatic shift to renewable energy," said Taylor McKinnon, public lands director for the Center for Biological Diversity, a Tucson-based environmental advocacy group."But where we put these facilities is important. We need to be siting them in a way that does not compromise endangered species."

The BLM briefly put a moratorium on solar applications this summer after being deluged by requests. The agency is assessing the environmental impacts of the projects. No proposal has made its way through the permitting process.

But as the push for renewable energy gains momentum - the government may have to start considering such projects with greater urgency.

One possible solution that has early appeal for both sides: locating such developments on old brownfield or Superfund sites.

In late September, the Environmental Protection Agency released a national database of contaminated sites, in various stages of cleanup, that might be ideal for reuse as a renewable-energy development.

The idea hasn't been studied in any detail, but both sides say it warrants further consideration.