But supporters of the bill acknowledged that it will be difficult to overcome a certain GOP filibuster threat against the legislation, meaning congressional action on global warming will probably be decided in the next Congress and by the next president.
Many of the GOP senators who voted to debate the issue have said they are opposed to the bill.
The Senate measure, which has wide Democratic and some Republican support, would cap US emissions of greenhouse gases, cutting them by 18 percent by 2020 and by two-thirds by midcentury. It would target refineries, power plants, factories, and transportation for 70 percent reductions and make emissions allowances available to be traded in an open market.
Senator Barbara Boxer, a Democrat from California and a chief architect of the 500-page bill, said at a news conference that the urgency of taking action against climate change cannot be overstated. "It's about our children, about their children, and about the planet we've inherited," she said.
Democratic leaders were ready to spend the week, and possibly more, on the legislation. But the tone of the debate emerged in the opening hours.
Republican leader Mitch McConnell of Kentucky called it "a giant tax on virtually every aspect of the economy," and accused Democrats of being "laughably out of touch" in taking up the bill when the country is reeling from $4 a gallon gasoline and other high energy costs.
President Bush said at a White House event that the measure amounted to "a huge spending bill fueled by tax increases" and that it "would impose roughly $6 trillion in new costs on the American economy."
White House spokeswoman Dana Perino said Bush would veto the bill as it stands, but said it seems unlikely the legislation will clear the Senate anyway.
The White House maintained that the carbon limits would "impose a huge new tax" and demand "drastic emission cuts that have no chance of being realized."
