* U.N. agencies to sign agreement on Africa food output

* Discord on biofuels may water down final declaration

* Mugabe accused of using food aid as election weapon

By Stephen Brown and Robin Pomeroy

ROME, June 4 (Reuters) - A U.N. summit on the global food crisis asked rich nations on Wednesday to help revolutionise farming in Africa and the developing world to produce more food for nearly 1 billion people facing hunger.

"The global food crisis is a wake-up call for Africa to launch itself into a 'green revolution' which has been over-delayed," Nigerian Agriculture Minister Sayyadi Abba Ruma said on the second day of the three-day summit.

"Every second, a child dies of hunger," he told Reuters. "The time to act is now. Enough rhetoric and more action."

The U.N. Food and Agriculture Organisation called the summit after soaring commodity prices threatened to add 100 million more people to the 850 million already going hungry and caused food riots that threaten government stability in some countries.

The cost of major food commodities has doubled over the last couple of years, with rice, corn and wheat at record highs. The OECD sees prices retreating from their peaks but still up to 50 percent higher in the coming decade.

U.N. Secretary-General Ban Ki-moon said the summit, attended by 151 countries, had shown "a clear sense of resolve, shared responsibility and political commitment among member states".

But discord over how much biofuels contribute to the rise in food prices, by competing with food output for crops, threatened to deprive the summit of a forceful final declaration.

"I doubt there will be a positive agreement on biofuels," said U.S. Agriculture Secretary Ed Schafer.

The United States, a leader in maize-based ethanol, and Brazil, the world's largest producer of ethanol from sugar cane, say it is important to diversify energy sources at a time when oil prices are sky-high and there is pressure for cleaner fuels.

BREADBASKET

Ban's predecessor at the head of the United Nations, Kofi Annan, was in Rome to sign an agreement with U.N. food agencies for a new drive to increase farm production in Africa.

"The world is facing an unprecedented world food crisis and nowhere is this crisis more serious and acute than in Africa," he said of the new plan.

"We hope to spur a green revolution in Africa which respects biodiversity and the continent's distinct regions," said Annan, who chairs the Alliance for a Green Revolution in Africa (AGRA) which is coordinating the effort.

He told Reuters that African nations using prime farm land for biofuel risked creating food shortages, adding, "they will regret it because the population will turn on them."

Among the problems African nations have is poor distribution of food because roads and railways built in colonial times lead to the sea rather than connecting crop regions inland, he said.

AGRA will give technical support to improve soil and water management, access to seeds and fertilisers, and infrastructure in "breadbasket" areas with relatively good farming conditions.

Nigeria's Ruma said his country had "the potential to become the food basket of Africa." But its farms were 90 percent dependant on rainfall, making them vulnerable to climate change, and its 14 million smallholders used rudimentary techniques.

Zimbabwe's Robert Mugabe, who told the summit that former colonial power Britain was to blame for many of his country's problems, was accused by a human rights group of using food aid as a weapon ahead of a June 27 presidential run-off election.

Human Rights Watch said he was blocking food being sent to supporters of opposition leader Morgan Tsvangirai and had "a long history of using food to control the election outcome."

U.N. High Commissioner for Human Rights Louise Arbour voiced concern, saying: "If true, this would be an unconscionable act." (Additional reporting by Phil Stewart and Alister Doyle in Rome and Paul Simao in Johannesburg; Editing by Robert Woodward)

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