The agreement, which calls for sharp reductions in heat-trapping greenhouse gases by the United States and 37 other industrial nations, was signed in New York and announced in Buenos Aires at a 160-nation environemental conference.
Signing the accord was largely symbolic since it must still be ratified by the Senate, something that is not likely anytime soon.
Congressional critics of the treaty this week cautioned the administration against signing the pact, saying that would further galvanize opposition in Congress.
Under the treaty, the United States had until March to sign. The Kyoto protocol has been signed by 60 countries, including every major industrial nation. It has been ratified by only one country, Fiji.
The administration has said it won't ask the Senate to consider the treaty for ratification until developing countries such as China agree to participate - and that could take several years.
But U.S. officials used the signing to energize the negotiations at the climate conference concluding this week. They hoped signing the treaty would help convince representatives from developing nations and Europe that the United States is taking the issue seriously.
On Wednesday, Argentina said it would take voluntary action to address climate change. The move was seen as a breakthrough by U.S. officials because Argentina would be the first developing nation to make such a commitment. China and India, two of the biggest sources of greenhouse gases, have steadfastly refused to make any such commitment.
The United States has been criticized by developing countries and Europeans for failing to curb greenhouse gases, mainly carbon dioxide from burning fossil fuels.
The signing, however, is expected to add fuel to the congressional debate over global warming.
In a letter to President Clinton this week, Sen. Robert C. Byrd, D-W.Va., had urged against a high-profile signing of the accord at this time.
"I urge you to resist making empty gestures that will only make the potential future approval of the (Kyoto) protocol by the Senate more difficult," Byrd wrote the president earlier this week.
Another Democrat, Rep. John Dingell of Michigan, canceled plans to attend the Buenos Aires conference because he expected the treaty signing. "The timing of this signing only encourages countries who refuse to be part of any effort to limit greenhouse gas emissions," said Dingell, a staunch opponent of the Kyoto accord.
The meeting in Buenos Aires, which is scheduled to wrap up Friday, is aimed at forging details of the climate protocol reached in Kyoto, Japan, nearly a year ago.
Under the Kyoto agreement the United States by 2008-2012 would have to roll back heat-trapping gases, principally carbon ioxide from burning fossil fuels, to below what they were in 1990. With economic growth, that would amount to cutting emissions by more than a third from what they normally would be.
By H. JOSEF HEBERT