"I have come to the conclusion that there will be a very good and concrete outcome (to the summit)," Klaus Toepfer, the head of the U.N. Environment Programme, told Reuters.

"Yes, I think we will have (an agreement)," he said on the sidelines of a symposium of judges discussing environmental law.

Environmental groups and others have warned that the summit's action plan is in danger of being so watered down that it will be meaningless.

Others believe that no plan will emerge, with the countries of the affluent North and impoverished South divided over timeframes and funding methods.

The World Summit on Sustainable Development (WSSD) - dubbed "Earth Summit II" - will be held in Johannesburg from August 26 to September 4. More than 40,000 delegates and over 60 heads of state are expected to attend.

South African Foreign Affairs Minister Nkosazana Dlamini-Zuma told reporters in Johannesburg this week that informal talks had narrowed the differences that existed in Bali but she did not elaborate.

Toepfer said sustainable development - a rather vague concept that broadly refers to maintaining or kick-starting economic growth without irreparably harming the environment - was closely linked to global security.

"Sustainable development is really at the centre of a peaceful world," he said.

"When we have ongoing tensions, ongoing differences between the rich and the poor and this gap is even widening, then we cannot expect (peace)," Toepfer added.

He said tension and conflict around the world would continue to rise if no firm commitments were made by heads of state at Johannesburg. He added that the summit would benefit if U.S. President George W. Bush were to attend.

Officials said last week Bush would skip the conference and that Secretary of State Colin Powell will lead the U.S. team.

"It's always very helpful to have the most important players," Toepfer said.

The summit aims to draw up a broad action plan to fight poverty and killer diseases like AIDS while providing clean water and sanitation to billions of people in the developing world.

Its five main themes will be water and sanitation, food security, energy, health and biodiversity.