WASHINGTON — Food prices have declined overall in developing nations but not much, according to data issued by the Food and Agriculture Organization of the United Nations. The agency has developed an interactive database of staple food prices on national markets in 55 developing countries. "While food prices have fallen internationally, as indicated by the F.A.O. food price index, this tool shows that in developing countries they have not fallen so fast, or at all," said Liliana Balbi, a senior economist with the Global Information and Early Warning System at the F.A.O. The agency noted that food costs account for 60% to 80% of consumer spending in developing nations, versus 10% to 20% in industrialized nations. The data may be accessed at http://www.fao.org/giews/pricetool/.