NAIROBI, KENYA - With the world's appetite for food expanding, sub-Saharan Africa, where nearly two-thirds of people make their living from farming, could be developing into an agricultural powerhouse.

But Africa's farms today are only one-fourth as productive as the world average. Populations are growing fast, while food productivity per capita has declined from 30 years ago. During that time, Africa has gone from a continent of food exporters to one that imports tens of millions of tons of it every year.

"These are farmers who are basically always living on the edge," said Josh Ruxin, a development expert at Columbia University. "They produce just enough food to eat, and during natural disasters or economic downturns they use up their crops and are thrust to the brink of hunger."

Experts say that Africa badly needs a "green revolution" like the one that lifted millions of farmers in Asia and Latin America out of poverty a generation ago with higher-yielding seeds and basic innovations such as fertilizer and improved irrigation. The vast majority of African farmers still tend their crops by hand, fertilizer use is one-tenth what it is in Asia, and less than 4 percent of farmland is irrigated.

A lack of basic infrastructure makes it expensive and time-consuming to transport goods to market, especially during fuel-price shocks.

Foreign donors have neglected Africa's farm sector in recent decades, shifting the bulk of development assistance to health and education projects. The U.S. government has cut agricultural aid to Africa by 75 percent over the past two decades, according to the Council on Foreign Relations, a nonpartisan research center.

In Burundi, where 91 percent of the population depends on agriculture, the government invests just 2 percent of its budget in the farm sector. That figure is even lower in other countries. African Union member countries pledged in 2003 to increase agriculture spending to at least 10 percent of their national budgets within five years, but only Rwanda and Zambia have followed through, the Council on Foreign Relations points out.

Former U.N. Secretary-General Kofi Annan said last month that African farm production should double within a decade. Agronomists caution against such rosy predictions, saying that African farmers may never catch up to their Asian or Latin American counterparts.

It may simply be enough, experts say, for African farmers to be able to feed themselves reliably and escape the clutches of poverty.

"What is clear is that if there's a green revolution in Africa, it's not going to look like the green revolution in Asia," Ruxin said. "It will not be about exporting huge amounts of food, but it will be about millions of people in Africa being able to feed themselves and to afford things like health care, education for their kids. And that in itself would be revolutionary."

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