JOHANNESBURG - World governments sit down together in Johannesburg on Saturday for negotiations that could well decide whether next week's mammoth Earth Summit ends in new global harmony or ugly recriminations between rich and poor.

Ten years after a first grand conference in Rio de Janeiro, many of its promises to narrow the yawning wealth gap without the environmental damage that has accompanied prosperity in the West have either been broken or, at best, remain unfulfilled.

"Since the Rio summit we have witnessed growing global inequalities as well as more migrations, epidemics, conflicts and instabilities," South African President Thabo Mbeki said on Friday as Johannesburg, a metropolis of gleaming prosperity and sprawling slums, prepared to welcome at least 40,000 delegates.

"We should ensure that by the time this summit finishes we have taken practical programs of action that bring hope to the millions of poor people across the world," he said.

If the world summit on sustainable development is to live up to the hopes of its United Nations organisers and revive Rio's green agenda, it will help if senior officials can narrow some serious differences before it formally opens on Monday.

Negotiators from the United States -- the world's richest power and biggest polluter -- can be counted on to lead stiff resistance this weekend to demands from developing nations for more aid and easier access for their produce to wealthy markets.

U.S. President George W. Bush, who will not join 100-odd other world leaders for the summit finale in 10 days time, has already angered many environmental lobbyists by pulling out of the Kyoto Pact that sets targets for the cutting the pollution blamed for global warming and extreme weather patterns.

*** U.S. Suspicions **** And while supporting the overall goals of alleviating poverty while preserving the health of the planet, Washington is deeply suspicious of fixing firm targets for performance that it fears could hurt the economy and be cheated on by other states.

It has also made clear it will not go along with attempts to open up new negotiations in Johannesburg on aid budgets and trade following deals cut in other, separate forums over the past year*** --*** at Monterrey, Mexico, on increased Third World aid and at a World Trade Organization (WTO) meeting in Doha.

"What we would like to see as we go into Johannesburg is not a rewriting of texts that had been agreed to," one senior U.S. official said in Washington earlier in the week.

Secretary of State Colin Powell will represent Bush in South Africa.

But developing countries point to UN figures suggesting aid must be much more than the $60 billion a year agreed at Monterrey to meet an agreed target of halving the proportion of the world's population living on less than a dollar a day by 2015.

African and Asian states are also angry at U.S. and European Union farm subsidies worth several times the total aid budget which, they say, denies their poor farmers access to markets.

"We think we will have a united front... we want more financial assistance from the developed world with time frames," said one North African delegate after officials from more than 100 developing states met to prepare tactics on Friday.