The text, to be debated at the summit, is supposed to outline ways to halve global poverty by 2015 while protecting the planet, but is stocked with fuzzy words saying nations will "strengthen", "encourage", "promote", "provide", "support" or "improve" policies, but makes few clear promises.

"There are only a few hard targets, and so much of it is unmeasurable, unverifiable statements of intent," said Stephen Peake, a lecturer at Britain's Open University who has worked on such documents for the United Nations in the past.

The 10-day summit opening on Monday, which organisers say will be one of the biggest U.N. gatherings, will draw more than 40,000 delegates and an expected 100 world leaders for what may be hair-splitting sessions about ways to improve policies on water, energy, health, agriculture and biodiversity.

Brackets inserted around contentious phrases earmark them for debate, drawing the battle lines between rich nations reluctant to make new commitments and poor nations pushing for clear timetables for better aid and trade.

Environmentalists say Washington is often the biggest brake.

"The U.S. have give a blanket 'No' to anything with any numbers in it," said Steve Sawyer of environmental campaigners Greenpeace, referring to the section of the document dealing with climate change.

IMPOSSIBLE TO PIN DOWN COMMITMENTS

Peake said the implementation plan for the so-called World Summit on Sustainable Development spread responsibility so wide that it would be impossible to pin down one state to any commitments.

"I was absolutely surprised when I picked this document up that it was so weak," he said. "The most common verbs are to "strengthen" and to "support", which are very weak verbs. How can you pin anyone down to these?"

Sawyer said there were a disappointingly small number of definite clauses in the draft action plan, upon which delegates failed to agree at the last preparatory meeting before the summit, held in Bali in June.

"Most of the document is full of unmeasurable, unmonitorable statements of intent," he added. "Unless there is some structure it will not strengthen the existing U.N. institutions."

He said activists were concerned that certain phrases were used very frequently without anyone being sure of their meaning.

"They use phrases like public/private partnerships, voluntary partnerships - it's all diplomatic babble, effectively amounting to nothing," he said.

Melissa Carey of U.S.-based group Environmental Defence said the scope of the summit had been broadened to entice the United States to participate, but that principle had weakened the potential to produce real results.

"A lot of countries agreed to play down climate change in the hope of getting broader participation from the U.S.," she said. "In the absence of one major topic ... it is easier to avert major specific commitments."

U.S. President George W. Bush, who will not attend the Johannesburg summit, pulled out of the Kyoto pact, meant to limit emissions of gases blamed for pushing up world temperatures, saying it was too expensive for the U.S. economy and was unfair because it excluded developing nations.

Secretary of State Colin Powell will represent Washington in Johannesburg.