The agency said the huge increase in the number of plans for solar power plants has caused worries about their environmental impact, The New York Times reported. Officials expect an impact study to take two years.

The moratorium affects millions of acres in Arizona, California, Colorado, Nevada, New Mexico and Utah. Officials said 130 applications to lease public land for solar projects have been filed since 2005.

The high price of oil makes solar power an attractive alternative, energy analysts say. Advocates say sun-drenched public lands in the Western deserts are a resource that should be used.

"It doesn't make any sense," said Holly Gordon, vice president for legislative and regulatory affairs for Ausra, a solar thermal energy company in Palo Alto, Calif. "The Bureau of Land Management land has some of the best solar resources in the world. This could completely stunt the growth of the industry."