United Nations ? The number of hungry people in the world increased during the last half of the 1990s by 18 million, to a total of 842 million, reversing a steady drop during the past three decades, according to a new study by a U.N. agency.

The Food and Agricultural Organization (FAO), which on Tuesday published the new figures in a report titled “The State of Food Insecurity in the World,” warned that the increase was undermining efforts by the United States and other governments to reduce the number of hungry people in the world to about 400 million by 2015. That goal was set at the 1996 World Food Summit in Rome.

More than one in seven people in the world endure chronic hunger, which is measured by a daily intake of less than about 1,700 calories and a lack of access to safe and nutritious food. The vast majority — some 798 million — live in poor, developing countries. About 10 million reside in the world’s wealthiest industrialized nations.

Despite the setback, the report’s chief author, Hartwig de Haen, noted that the scale of world hunger had fallen dramatically over the past quarter-century. The share of the developing world’s population facing chronic hunger decreased from 37 percent in 1970 to 17 percent in 2000, he said.

Even throughout the 1990s, the overall number of hungry people fell by 19 million, thanks to an initial drop of 37 million in the first half of the decade.

Nineteen countries, including China and Brazil, achieved a decline of 80 million chronically undernourished people over the decade. China alone, which has experienced economic growth in the 1990s, reduced the number of hungry people by 58 million.