The U.S. Agriculture Department said the number of hungry people in 70 poor nations soared 10.8% last year and will climb at least 1.7% this year, and perhaps much more depending on how the global recession plays out.

The annual USDA survey, which attempts to calculate how many people are consuming less than 2,100 calories a day in countries that do or did receive food aid, is ammunition for the Obama administration in its push to help poor nations feed themselves.

The White House is requesting that Congress double annual spending on foreign agricultural development aid to roughly $1 billion in 2010. Secretary of State Hillary Clinton, who is steering an inter-agency task force formulating the U.S. strategy on global hunger, is calling agriculture development a “central element” of U.S. foreign policy.

According to the USDA, the number of hungry people in its survey hit 819 million last year, up from a revised 739 million in 2007, as soaring grain costs put food out of the reach of many poor people, sparking riots in dozens of countries.

According to Stacey Rosen, a USDA economist who is a co-author of the report, half of Sub-Saharan Africa’s population is undernourished, giving it the highest prevalence of hunger in the world.

The global food crisis faded from view when Wall Street’s swan dive splashed cold water on grain prices late last year. But the contraction of the global economy is offsetting any benefit for many of the world’s poor. Their ability to buy food is shrinking faster than food prices. With trade and foreign investment in many poor countries slowing, millions of jobs are evaporating. And many of the jobs disappearing in the rich world were held by immigrants, who are sending less money home.

USDA economists figure that the number of hungry people in the 70 countries will likely climb to 833 million this year. But the agency is warning that the number would soar if the recession significantly cools global demand for the developing world’s raw materials and the credit crunch shrinks its ability to finance imports of goods such as food.

Under the department’s grimmest scenario, the number of hungry in its survey would rise to 930 million this year, up 13.6% from 2008.

In June, economists at the United Nations’ Food and Agriculture Organization in Rome predicted that the number of people going hungry every day around the world will hit 1.02 billion this year. The FAO estimate is broader than the USDA’s 70-country survey, which doesn’t include nations such as China, and the FAO defines hunger differently than the USDA.

Write to Scott Kilman at scott.kilman@wsj.com