The U.S. Fish and Wildlife Service recommends designating up to 1.8 million acres in 28 California counties as habitat critical to the frog's survival. The proposal must undergo 60 days of public comment and another review before it becomes final.
The designation would require any development project on the land to get prior approval from federal wildlife officials.
"The goal of the service is to help recover this species," agency spokesman Mike Fris said in a statement.
The red-legged frog has the largest population of any frog native to the western United States. The species is believed to have inspired Mark Twain's tale, "The Celebrated Jumping Frog of Calaveras County." It was listed as a threatened species in 1996.
The frog's native habitat includes coastal areas of California, the Sierra Nevada foothills, the Central Valley and other wet areas stretching from Mendocino County to Los Angeles. Federal wildlife officials say the frog once lived in 46 counties but now remains in only 31.
If approved, the Fish and Wildlife Service's proposal would be the first critical habitat expansion since the agency announced last year that it would reverse seven rulings that denied endangered species increased protection, said Jeff Miller, a conservation advocate with the Center for Biological Diversity.
The reversals came after an investigation found an Interior Department official had pressured government scientists to alter their findings about several species, including the red-legged frog.
The agency in 2006 designated 450,288 acres of critical red-legged frog habitat- a fraction of the 4.1 million acres initially recommended by agency scientists in 2001.
In the 2006 rule, the agency said protecting 450,000 acres would cost $498 million in lost development opportunities over 20 years. The agency said it was studying the economic impact of its newly expanded habitat proposal.
"It would have a potential to have a devastating impact," said Paul Campos, general counsel at the Home Builders Association of Northern California. "Land prices in California and land holdings are historic lows, and there's not a day that goes by without either a builder or a lender or an investor going bankrupt. There couldn't be worse timing for this regulatory overkill."
The land proposed for critical habitat in the latest recommendations includes sections of two military bases, Vandenberg Air Force Base and Camp San Luis Obispo.