WASHINGTON - Flying by helicopter over the Hayman fire in Colorado earlier this month, national forest chief Dale Bosworth spied a swath of green persisting amid the orange flames. The green, it turned out, was a section of Pike National Forest that federal officials had thinned last year and treated with a controlled burn to prevent catastrophic forest fires. When the devastating fire reached that section of the forest it diminished, burning what little underbrush remained and failing to ignite the tall trees. That not only spared the big ponderosa pines but also gave Bosworth ammunition to argue for more active management of Western forests. Now Bush administration officials and some members of Congress hope that the fires raging in Arizona and Colorado will be a catalyst for a massive campaign of thinning and clearing trees and underbrush in Western forests. "It does work," Bosworth said in an interview. "We just need to get the public's support to do it more aggressively." Since the 1920s, the federal government has extinguished low-intensity fires, which burn underbrush and small trees. But it has allowed timber harvests of the largest trees, which are least susceptible to fire. The result is that the forests across much of the West are crammed with undergrowth and small trees, the ideal fodder for fire on a scale that was not imaginable a few decades ago. "The fires we're having now are not natural fires," said Mark Rey, who as Agriculture Department undersecretary oversees the National Forest Service. "The stands are so dense and the amount of fuel -- wood -- is so large that the fires are burning destructively and catastrophically." Some 70 million to 80 million acres have to be thinned to prevent the kind of colossal fires that have menaced the West in recent decades, Rey said. But at the rate the federal government is moving now -- about 2 million acres a year -- that process would take many decades. That the forests should be thinned is not so controversial as who should thin them. The Bush administration favors the timber industry for its know-how and because it could use the profit from whatever wood it removes to offset costs. Environmentalists, suspecting the industry of wanting to cut the big trees and leave the undergrowth, prefers the government do the job. Congress has approved money for small-scale thinning and controlled burns by federal foresters and local contractors, such as occurred last year in Pike National Forest. The Bush administration is proposing to hire timber companies to remove underbrush from forests along with enough marketable trees to make the effort pay off -- as long as they leave the largest and oldest trees behind. Payment for the cleanup would take the form of timber rather than taxpayer funds. Rey and Bosworth complain that the Forest Service has been stymied by some environmental groups, which suspect the administration of using fire protection to screen its real objective: increasing commercial logging. "If we really care about these forests, this has to be our top priority," Rey said. "We have to stop being sidetracked." Sen. John McCain, R-Ariz., who agrees, recently urged a number of environmental groups to suspend their suspicions and support Forest Service efforts to thin forests and prevent forest fires. The only way to thin the forests quickly enough to protect people is to let timber companies earn a profit while they do the job. "We don't have enough money to have the government fund it," McCain said. "You probably have got to have commercial operations doing this, and have them make some money off the deal." Environmentalists charge that timber companies for decades have stripped national forests of old-growth trees, damaging habitats and ecosystems. Sean Cosgrove, national forest policy specialist for the Sierra Club, said he did not trust commercial logging firms. "They'll claim to do fuel reduction and in the process take out commercial timber," he said. "They're going to take out more commercial timber than flammable brush." Cosgrove favors using only federal funds for the projects. He stressed that the Forest Service should not aim to thin and treat all the forests, only those closest to communities. "It's not a good spending of resources to thin all 140 million acres of national forests with trees," Cosgrove said. "The priority should be protecting lives and communities."