WASHINGTON - President Bush weighed in yesterday against a Senate bill that would require dramatic cuts in greenhouse pollution, cautioning senators "to be very careful about running up enormous costs for future generations of Americans."

The Senate climate bill, expected to be debated much of this week, would cut permitted levels of emissions of carbon dioxide from burning fossil fuels and other greenhouse gases about 70 percent over the next four decades. The bill targets power plants, refineries, factories, and transportation.

Supporters argue that the shift away from fossil fuels can be made without significant economic damage and that failure to address global warming itself would produce greater economic harm later this century.

Bush said the Senate bill "would impose roughly $6 trillion in new costs on the American economy." The president in the past had expressed opposition to mandatory limits on carbon dioxide and other pollution linked to global warming.

"There's a much better way to address the environment than imposing these costs . . . which will ultimately have to be borne by American consumers," said Bush, who has favored voluntary efforts and technology innovation to address global warming.

White House spokeswoman Dana Perino said Bush would veto the bill as it stands, but said it seems unlikely the legislation would clear the Senate anyway.

The Senate bill assumes getting $6.7 trillion over the next four decades from the sale and trading of carbon-emissions allowances in order to meet the imposed emissions caps.

Under the bill, the money would be used to help industries comply with the carbon reductions and to help people pay for higher energy costs.

About $800 billion over 40 years would be earmarked for tax breaks to help people pay energy costs.