HELENA, Mont. — The cost of fighting large fires in California and elsewhere is forcing the U.S. Forest Service to divert hundreds of millions of dollars set aside for work including roads, trails, recreational improvements — even fire prevention.

In a memo this month to regional foresters, Forest Service Chief Abigail Kimbell said spending on fires could reach $1.6 billion this year, about half the agency's budget.

"All of you are aware of the serious nature of this year's fire season and the issues faced by the agency in paying for fire suppression costs," Kimbell wrote. "At this time the only option for financing the shortfall is to use the agency's transfer authority."

The memo makes no mention of layoffs but cautions officials to be "use prudent cost-saving judgment" in hiring and in approving non-critical overtime.

The agency started transferring money in the middle of August and expects to take a total of $400 million from other areas through the rest of the fiscal year, which ends Sept. 30. Such transfers have occurred several times since 2000.

Environmentalists predicted fire spending could end up being closer to $2 billion, and transfers could run as high as $700 million. Among those programs seeing cuts are fire prevention and safety.

"We are robbing the Peters to pay the Pauls," said Chris Mehl, spokesman for The Wilderness Society's Northern Rockies Office in Bozeman. "The unfortunate thing is that it is across the board."

Money will be coming from restoration projects, building maintenance, land acquisition plans, research and other areas. In South Dakota, the Forest Service has closed a visitor center in the Black Hills National Forest early to save money.

Spending on all non-critical items for the rest of the year must be curtailed, Kimbell told foresters.

"I recognize that this direction will have a significant effect on agency operations," Kimbell said in the memo. "However, we must be in a position to protect life and property from wildfire, and do so within the funds available to the agency."

U.S. Sen. Max Baucus, chairman of the Senate Finance Committee, said he was not pleased to hear of the cuts and is pushing for a special account to pay for firefighting costs.

"The fire season in Montana and across the country is far from over. Not to mention we have good-paying jobs to fund and projects around the state that need to be completed," said Baucus, D-Mont. "Funding should not be pulled from our state's resources to help pay for fighting fires in California."

Forest Service funds allocated to fighting fires have steadily increased, rising about 10 percent from 2006 to 2007, but have not been able to meet the needs of this year's large fires, said Rose Davis, spokeswoman for the agency's northern region.

Mehl, of The Wilderness Society, said he likes the idea of Congress setting up separate budgets — one for fires and one for normal Forest Service operations. The group said fighting fires could surpass 50 percent of the Forest Service budget this year and is quickly dominating work at the agency.

"The costs are high, and they need to suppress these fires to protect people," Mehl said. "But the Forest Service is basically becoming the fire service."