Josette Sheeran, head of the Rome-based United Nations organization, will canvass administration officials, members of Congress, and others in a U.S. mission that begins on Wednesday, the WFP said in a statement, as she seeks to fill a $500-million shortfall for 2008 food aid donations.

The global aid community has been reeling in recent months as it seeks to stretch flat aid budgets to keep pace with commodity and fuel prices, which have soared along with booming biofuel demand, growth in developing nations, and lackluster harvests.

Last year, the WFP sketched out a $2.9-billion budget for its aid projects in 2008. It now says it will need $3.4 billion to cover the same aid work.

The WFP hopes the United States, the world's largest donor of food aid and also the WFP's largest backer, can help cover at least some of that shortfall.

Sheeran is due to meet with Rep. Jerry Moran, a Kansas Republican who is co-chair of the House Hunger Caucus, and other members of the House of Representatives, along with aides to Sen. Patrick Leahy, the Vermont Democrat who chairs a Senate subcommittee on foreign operations.

U.S. food aid officials are grappling with the same cost challenges.

Earlier this month, the largest U.S. food aid program, Food for Peace, said the cost of the food it donates had jumped 41 percent in the first half of fiscal 2008, forcing it to divert money destined for future aid to pay for past donations.

The Bush Administration has requested $1.23 billion for emergency food aid programs for fiscal 2009. Congress also is debating food aid policy as part of a five-year agriculture law that could be approved soon.

The run-up in commodity and shipping costs comes just as many poor countries struggle with rising food prices. The WFP expects that nations like Haiti, Djibouti, Zimbabwe, Chad, Yemen, Cuba and Myanmar will be hardest hit.

Sheeran, a former Bush administration official who took over last year at the WFP, will make a similar appeal in Brussels following her U.S. visit, the WFP said.