The Bush administration on Friday unveiled plans for a high-level conference on global warming in September that would bring together the world's biggest polluters to seek agreement on reducing greenhouse gas emissions.

U.S. President George W. Bush issued invitations to 11 other countries plus the European Union and the United Nations to attend the September 27-28 meeting in Washington intended to work towards setting a long-term goal by 2008 to cut emissions.

Bush had proposed the conference, which will be hosted by U.S. Secretary of State Condoleezza Rice, in late May before a summit of the Group of Eight industrial nations in Germany, but had withheld details until now.

In a letter to invitees obtained by Reuters, Bush assured them that the United States is committed to collaborating with other major economies to agree on a global framework for cutting greenhouse gas emissions.

But a senior U.S. official said the administration stood by its opposition to mandatory economy wide caps on emissions.

Bush agreed with other leaders of the G8 in June to make substantial but unspecified reductions in climate-warming emissions and to negotiate a new global climate pact that would extend and broaden the Kyoto Protocol beyond 2012.

But Bush has refused to sign up to numerical targets before rising powers like China and India make similar pledges. Convincing them to join the U.N. process will be crucial to reversing a rise in global temperatures.

China and India are among the countries invited to the September conference, which will also include Japan, Canada, Brazil, South Korea, Mexico, Russia, Australia, Indonesia and South Africa, the U.S. official said.