The August 26-September 4 summit is being billed as the largest U.N. meeting in history with more than 100 world leaders and 60,000 delegates expected to attend.

But following the collapse of preparatory talks in Bali, Indonesia, in June, agreement has yet to be reached on its main goal - the drafting of a detailed plan for global economic development that preserves and protects the environment while battling hunger and poverty.

Nitin Desai, U.N. undersecretary-general for economic and social affairs, said representatives of the United Nations' 189 member-nations had so far agreed on about 75 percent of the blueprint's text.

He predicted differences could be overcome before the summit began if delegates showed the necessary will. "I would not describe the conflict as insurmountable," he said.

MBEKI PICKS 25 FRIENDS

The group of 25 nations designated by South African President Thabo Mbeki as "friends of the chair" would be working between now and the summit's start to try to resolve the remaining differences, he added.

Desai was heading to Paris this week for talks with South African Environment Minister Mohammed Valli Moosa and Emil Salim, the former Indonesian environment minister who chaired the summit's preparatory meeting in Bali.

The Thursday talks were taking place at the Paris offices of the Organization for Economic Cooperation and Development.

The 25 nations due to attend next week's wider gathering in New York includes the Group of Eight industrialized nations Britain, Canada, France, Germany, Italy, Japan, Russia and the United States as well as Argentina, Brazil, China and Denmark.

Others due to attend were Egypt, Ghana, India, Indonesia, Jamaica, Jordan, Mexico, Nigeria, Norway, Senegal, Sweden, Uganda and Venezuela.

The Johannesburg summit is meant to build on the 1992 Rio de Janeiro Earth Summit, which set out global goals for environmental protection including a pledge to fight global warming in a deal since undermined by a U.S. pullout.

It also aims to lay out a path for achievement of the Millennium goals set out by the U.N. General Assembly at a landmark 2000 summit. These include halving world poverty and hunger, achieving universal primary education and halting the spread of AIDS by 2015.

Some critics say the summit is trying to solve too many of the planet's problems at one time - an almost inevitable recipe for failure.