By Alex Kirby BBC News Online environment correspondent

The world is now in earnest about working to end poverty, according to the United Nations official running the Earth Summit, Nitin Desai.

He believes the meeting will succeed, despite criticism of its huge and unwieldy agenda.

A decision by President Bush to attend would be "a very important indication of support".

Mr Desai said the way the world was developing lent the summit an unmistakeable urgency.

He was speaking to BBC News Online about a report, Global Challenge, Global Opportunity: Trends in sustainable development, published by the UN department of economic and social affairs. Mr Desai heads the department.

He is also secretary-general of the World Summit on Sustainable Development, starting in Johannesburg on 26 August.

Development is now as sexy as the environment

Nitin Desai

Mr Desai said the report's inescapable message was the urgency of reversing the present trend towards an unsustainable future.

He said: "The second message for Johannesburg is that we have to look at all these problems as a package and act on all of them simultaneously.

Only connect

He insisted there was a new seriousness about ending the abject poverty of hundreds of millions of people, though he acknowledged that the rich world still tolerated preventable mass child mortality.

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"We don't bother to prevent those deaths because we don't make the connections", he said.

"We think of health in terms of therapeutics, not public health.

"But I think the political will is there. Development is now as sexy as the environment, absolutely."

Mr Desai rejected any suggestion that the summit agenda was overcrowded.

"I ask people: 'What do you want to drop?'", he said. "I don't get an answer - because the issues are all so closely linked."

"I see a lot of commitment, and the countries involved have invested so much, they'll find a way. I'm pretty hopeful.

"If Mr Bush decided to come, that would be a very important indication of support. But the US is very heavily involved anyway.

The report lists some encouraging advances. The average number of children born by women in developing countries has fallen in 30 years from more than six to under three.

A continent left behind

Poverty is falling in Asia and Latin America, and hunger is slowly declining: about 800m people are chronically malnourished, 40m fewer than in 1990.

The number of under-five-year-olds dying from diarrhoeal diseases is estimated to have fallen from 4.6m annually in 1980 to 1.7m in 1999.

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But it lists some ominous trends too. Indoor air pollution kills more than 3m people a year, mainly children in poor countries.

Africa contends with increasing rates of malaria, as well as "by far the leading cause of death" south of the Sahara, HIV-Aids.

Its forests are vanishing at 7% each decade, Latin America's at 5%. An estimated total of 90m hectares of global forests was destroyed in the 1990s, an area larger than Venezuela.

Pressure for food

Most deaths in the poorest countries are from communicable, environment-related diseases, and could easily be prevented.

More than 1bn people lack access to safe water, and 2.5bn do not have adequate sanitation.

Food production and consumption are rising. And it is producing food that drives the depletion of natural resources.

Hungry countries will rely increasingly on food imported from Europe and North America.

Water shortages are growing: by 2025 they will affect about half the world's people.

There are "many signs of climate change". World population is growing, and demands for higher living standards: together they "will pose enormous strains on natural resources".