JOHANNESBURG, August 25 (News Agencies) - Diplomats were meeting behind closed doors in Johannesburg Sunday, August 25, on the eve of the U.N. Earth Summit in a last-ditch effort to save it from widely predicted failure as police cracked down on criminals and protesters.

Eight thousand extra police and an undisclosed number of troops have been deployed in and around the plush northern suburb of Sandton, where the 10-day World Summit on Sustainable Development (WSSD) will be held.

They are patrolling on mountain bikes and horseback, and the security services say they are prepared for air and mortar attacks, as well as snipers.

The police said Sunday they had arrested 278 people over the past 48 hours in swoops in Johannesburg, seizing arms, drugs, and stolen goods.

On Saturday, August 24, police fired stun grenades at around 500 anti-globalization protesters during an unauthorized march against the summit. Three demonstrators received minor injuries, organizers said.

The demonstrators - from around the world - gathered in front of Johannesburg’s University of The Witwatersrand to demand the right to protest at the summit when they were confronted by around 50 police in riot gear, who fired the grenades without warning.

The protesters, who said the summit was promoting globalization, retreated after lighting candles and placing them around the police’s feet, and burning official summit pamphlets.

The diplomats, from more than 30 key countries, are trying to resolve crucial disagreements between rich and poor nations and between the United States and Europe on the three pillars of sustainable development - poverty alleviation, social progress and protection of the environment.

Some 1,500 ministers from around the world will do the negotiating at the summit proper, with around 100 heads of state or government arriving for the final two or three days.

A notable absentee will be U.S. President George W. Bush, who is sending Secretary of State Colin Powell in his place - a decision that has angered the thousands of activists in Johannesburg.

Dutch Environment Minister Jan Pronk, a special envoy of U.N. Secretary General Kofi Annan, said he was confident the summit would produce a “credible” action plan despite the wrangling.

“I expect results,” he told reporters Sunday. “There will be an agreement and a commitment to implement an agreement which is credible.”

Pronk said he was “pessimistic after Bali but now I am optimistic.”

A preparatory meeting in the Indonesian resort island resulted only in “finalizing 70 percent of the text,” with major areas of disagreement in the remaining 30 percent, Pronk said.

However, subsequent informal meetings in Rio de Janeiro, Paris and New York, had helped in “creating a political understanding that can translate into a text,” he said.

A major disagreement is over objectives for poverty relief, which the European Union says are indispensable but which the United States refuses to endorse, in line with its reluctance to enter into any new multilateral deals.

Pronk said the follow-up to the first Earth Summit in Rio de Janeiro in 1992 was poor on the whole, especially with poverty having increased dramatically in the 1990s despite “higher growth than in the 80s, 70s, 60s or 50s”.

He said Bush’s absence from the summit was a “bad sign”.

“I regret it. We had really done a lot to push the invitation,” he said. “However Colin Powell is coming... and he is one person in the American administration who has really shown a vision oriented towards sustainability. That is a good sign."

Pronk said he had found “quite an interest in sustainability" during talks with U.S. officials,” which gave him hope.

“Since September 11 last year the paradigm of security is overwhelming,” he said.

Scientists worldwide, including 30 Nobel Prize laureates, meanwhile united for the first time Sunday to appeal to leaders at the summit to protect the planet to avoid disaster.