The increasing diversion of food and animal feed to produce biofuel, and sharply higher fuel costs have also helped to shoot prices upward, experts say.

The United Nations is encouraging summit participants to start undoing a decades-long legacy of agricultural and trade policies that many blame for the failure of small farmers in poor countries to feed their own people.

Wealthy nations' subsidizing their own farmers makes it harder for small farmers in poor countries to compete in global markets, critics of such subsidies say. Jim Butler, the FAO's deputy director-general, said in an interview ahead of the gathering that a draft document that could be the basis for a final summit declaration doesn't promise to overhaul subsidy policy.

Congress last month passed a five-year farm bill heavy on subsidies, bucking White House objections that such aid in the middle of a global food crisis wasn't warranted.

The head of the summit's U.S. delegation, Agriculture Secretary Ed Schafer, insisted on Monday that biofuels will contribute only 2 or 3 percent to a predicted 43 percent rise in prices this year.