Swedish Environment Minister Kjell Larsson said the 1972 Stockholm gathering was "the first conference that focused on global environmental issues".

But celebrations will be tempered by frustratingly slow progress in the past three decades. "We believed that we could solve the issues quicker at that time," Larsson said, recalling the heady 1972 mood.

The talks will give a chance to discuss stalled preparations for a new U.N. summit in South Africa in August aimed at fighting poverty while saving the planet.

Hopes for the Johannesburg summit, seeking to halve the number of people living in poverty by 2015 while curbing pollution, faded earlier this month when a preparatory ministerial conference in Indonesia broke up after 120 ministers failed to agree on a 158-point action plan.

DIPLOMATIC LOBBYING

The 1972 meeting followed years of diplomatic lobbying in the United Nations led by Sverker Astrom, one of Sweden's most renowned diplomats.

The whole idea was met by suspicion by several blocs. Developing nations, for instance, considered environmental degradation to be a problem only for industrialised states as well as the Communist bloc, Astrom said in his memoirs.

Astrom also said some Western countries such as Britain and France were reluctant as they worried about the costs of such a conference and suspected developing countries could use it to demand more aid. Such disputes still rage today.

In his memoirs he recalls a comment by a Japanese delegate at the time: "It is possible that what you call environmental problems can be found in other countries, and you are welcome to talk about them. But we do not have any such problems."

Larsson said the meeting was "the starting point of a very impressive development in terms of the number of environment conventions, environment ministries and huge growth of environment non-governmental organisations".

The 1972 meeting helped lead to the creation of the U.N. Environment Programme (UNEP) and included landmark calls for global cooperation on combating pollution.

Among delegates in Stockholm will be Canada's Maurice Strong, who led the 1972 conference and a follow-up Earth Summit in Rio de Janeiro in 1992, and Klaus Toepfer, head of UNEP.

Three decades of cooperation have generated positive results, such as a huge drop in sulphur dioxide emissions due to tough environmental laws and economic incentives, and improvements in water quality, at least in rich nations.