But the pact, approved by delegates from 150 nations, immediately was denounced by Republican critics in Congress who predicted it would never be ratified by the U.S. Senate.
Diplomats worked through the night to finish the agreement, which for the first time will commit nations to rolling back emissions _ carbon dioxide from burning fossil fuels and five other atmospheric gases _ to pre-1990 levels.
Vice President Al Gore, who energized the talks during a one-day trip to the conference when he signaled to U.S. negotiators the need for deeper emissions reductions, said the agreement "lays a solid foundation for long-term efforts to protect our climate."
In New York, President Clinton called the accord "a huge first step" for dealing with what an overwhelming number of scientists believe is a threat to the Earth's climate because of warming caused by heat-trapping gases.
"I did not dream when we first started that we would get this far," Clinton said.
The accord calls for the United States to reduce greenhouse gases to 7 percent below what they were in 1990, deeper cuts than originally proposed. Europe and Japan would make cuts of 8 percent and 7 percent, respectively, below 1990 amounts. The reductions would be achieved between 2008 and 2012.
Such reductions would require U.S. businesses and consumers to use substantially less energy and redirect the country's energy policy to encourage a shift away from burning coal and oil, which have high carbon content.
President Clinton had originally proposed that emissions be cut only to, not below, 1990 levels. The European Union had favored a more ambitious plan: cutting emissions by 15 percent below 1990 levels by 2010.
Because of expected economic growth, the treaty's emissions caps are unlikely to be met unless U.S. industry and consumers slash energy use and lower carbon dioxide emissions by about one-third from where they would otherwise have been, the Energy Department has estimated.
Clinton administration officials _ as well as most environmentalists _ maintain that such reductions can be achieved by developing new energy-efficient technologies, and through renewed emphasis on conservation. Over the next 12 years, numerous ways can be found to reduce carbon emissions without imposing energy taxes, they argue.
Clinton has promised to commit $1 billion a year over the next five years to boost energy efficiency and clean-technology programs, although White House budget officials have yet to pinpoint where the money would come from.
Rep. James Sensenbrenner, R-Wis., a congressional observer at the Kyoto talks, questioned whether Congress can afford such a program as it continues to press for budget deficit reduction.
Congressional critics of the Kyoto Protocol argue it would lead to soaring energy costs that will force businesses to move to developing countries that are not _ for the time being _ bound by the same emissions ceilings.
In Washington, Senate Majority Leader Trent Lott, R-Miss., said the Senate "will not ratify a flawed climate treaty."
Sen. Chuck Hugel, R-Neb., one of the pact's sharpest critics and another member of the observer team, added, "There's no way we'll even be close in the Senate to ratifying this agreement. We will kill this if the president signs it."
Hugel was co-sponsor of a resolution passed 95-0 earlier this year calling for rejection of any treaty that does not include participation by developing countries such as China.
In the contentious final session, the United States failed in its main effort to extend binding commitments to developing countries, a provision that would have allowed Third World nations to "opt in" under mandatory reductions.
U.S. chief negotiator Stuart Eizenstat said "the biggest challenge in the next several years" was to work for getting the developing countries on board.
"It is essential," said Clinton during a stopover in New York, "that these nations participate in a meaningful way if we are to truly tackle this global environmental challenge."