"Yet these gains are threatened by catastrophic wildfires," Feinstein, D-Calif., told more than 100 people gathered at the 12th annual Lake Tahoe Forum.

California is already straining from the effects of a series of wildfires that have scorched more than 1 million acres in California alone this year and cost the state nearly $300 million to fight.

The Lake Tahoe Restoration Act was funded from sales of public lands in the Las Vegas area. Feinstein said she hopes the new proposal will also be around $1 billion.

The second phase would focus on reducing particulate matter and algae in the lake, two agents that can seriously harm Tahoe's legendary clarity. It also would seek to reduce the risk of catastrophic wildfires fueled by dense forest areas and a lack of defensible space around homes in fire-prone areas.

"I shudder to think what will happen if we don't move aggressively to build those firebreaks, remove those dead and dying trees and clean out as much underbrush as possible," Feinstein said.

Researchers at the University of California, Davis' Tahoe Environmental Research Center reported last week that the lake's clarity improved slightly in 2007, to a depth of 70 feet, up from 64 feet when the joint preservation efforts began in 1997. Still, it's a far cry from the 102 feet scientists reported seeing when measurements began in 1968.

Feinstein and Kempthorne appeared with Senate Majority Leader Harry Reid, D-Nev., and Nevada Gov. Jim Gibbons.

Kempthorne signed an order releasing another $140 million from the Southern Nevada Public Land Management Act, about $54 million of it for projects around Lake Tahoe. That includes $24 million for watershed and habitat improvement, science and research and air quality; and $30 million for the Lake Tahoe Environmental Improvement program.

But despite the progress, researchers said global climate change continues to pose serious threats to the once-pristine wilderness.