President Clinton announced goals for capping US greenhouse gas emissions which fall short both of targets proposed by Japan and the European Union and of those he himself set four years ago.
The plan to reduce emissions, blamed for global warming, to 1990 levels between 2008 and 2012, and to undertake further cuts over the ensuing five years, appears designed to satisfy both environmentalists and the powerful US industrial lobby.
"We simply must commit to binding limits," Mr Clinton said at the National Geographic Society headquarters where he unveiled his long-awaited policy.
But he made US engagement conditional on pollution limits in the developing world, especially in rapidly industrialising countries such as Brazil, China, India and Mexico.
Mr Clinton's proposals had been impatiently awaited by delegates from about 150 countries gathered at a conference in Bonn to work out a treaty on climate change in advance of a December summit in Kyoto, Japan, when a cap on greenhouse gas emissions is expected to be fixed.
In calling for a reduction of emissions to 1990 levels between 2008 and 2010, and by 2012 at the latest, Mr Clinton pushed back his own 1993 goal - for 1990 levels to be reached by 2000 - by at least eight years.
But his adviser on the environment, Ms Kathleen McGinty, described the new goals as "significant." She said: "It represents a 28 per cent reduction in US emissions from where they would otherwise be."
Mr Clinton's plan provides for a $5 billion dollar programme, in the form of tax breaks and research credits, to encourage US companies to cut emissions. But it does not identify specific figures for reductions after 2012.
In Bonn, UN spokesman Mr Axel Wustenhagen said the conference would be the "eighth and final round of negotiations to strengthen the convention on climate change adopted in 1992" in Rio de Janeiro, at the first world environmental conference.
The Rio convention called for member states to reduce emissions of greenhouse gases by the year 2000 back to the levels of 1990. But a conference in Berlin in 1995 called for stronger measures.
The EU has proposed a reduction of 15 per cent of the 1990 levels by 2010, while Japan has proposed a five percent reduction from 2008 to 2012.