(FORTUNE Magazine) – The United Nations Conference on Environment and Development (Unced) that convenes in Rio de Janeiro on June 1 will be the largest such assemblage ever. Besides all the U.N. nations, thousands of interest groups ranging from the Greens Union of Armenia to the World Society for Prevention of Cruelty to Animals will samba into Rio for an unprecedented Earth Summit. The International Chamber of Commerce is trying to preempt the proceedings by holding its own Rio conference in May. Its 7,000-member associations and companies, including Du Pont, General Motors, and Glaxo Holdings, want their prescription for balancing environmental protection and economic development to be heard first. But early drafts of their positions don't go far toward resolving the conference's key issues (see table). The main sticking points are the transfer of environmental technology and financial resources to developing countries in the Southern Hemisphere from industrialized ones in the North. Both sides have reason to be stubborn. U.S. businesses want to get a fair return on investments and protection of patent rights, while the developing nations are eager to gain economic strength and to somehow preserve the environment at the same time. Says Dante B. Fascell (D-Florida), chairman of the House Foreign Affairs Committee: ''The developing countries are pointing their finger at the industrialized ones, saying, 'You guys fouled up the world, and now you're trying to correct it at our expense.' Meanwhile, the U.S. appears to be laying back because we don't want to get sucked into the vortex of financial commitment.''

CHART: NOT AVAILABLE CREDIT: MARIA KEEHAN FOR FORTUNE CAPTION: ON THE TABLE AT THE ENVIRONMENT SUMMIT