Giant bags of cornmeal, labeled "USA" for the country that donated them, sit stacked 40 high in a U.N. warehouse on the outskirts of this city. Together with the cooking oil, beans and high-protein meal for porridge also stored here, there is enough to feed hundreds of thousands of people.

But there is no plan to do so.

President Robert Mugabe, the only ruler Zimbabwe has had in the 24 years since the end of white rule, has announced that a bumper harvest will produce more than enough food for the country this year, for the first time since 2000.

That means officials of the U.N. World Food Program, which like other aid groups operates only at government request, have little choice but to ignore the evidence around them -- the brown and withered fields, the beggars on the street and the hungry faces in townships less than a mile from the warehouse, one of several the United Nations maintains in Zimbabwe.

So the World Food Program and other international aid groups here are in retreat. They are cutting staff, dismantling their distribution networks and wondering who, if anyone, will help Zimbabweans who have relied on U.N. feeding centers over the past three years. At the peak in 2003, the U.N. facilities fed more than 6.5 million people, more than half the nation's population of 12 million.

"We have to accept the government's forecasts of a bumper harvest," said Mike Huggins, a spokesman for U.N. feeding programs in southern Africa. "We only hope that people with no source of income will be able to access some of that surplus."

Few independent observers here believe there will be a surplus. In June, U.N. special envoy James Morris warned that as many as 5 million people in the country may need food aid in the coming year.

Mugabe's government has restricted information, shut down newspapers and criticized people who disagree with its pronouncements. In May, it suspended the crop estimate program conducted annually by the government in concert with U.N. officials.

Mugabe has attacked aid groups as a threat to his party and made clear his willingness to expel them if they defy his wishes. A cabinet minister last month told provincial governors they should not hesitate to tell groups that fail to coordinate their activities with the government "to pack their bags and go," according to the government-run Chronicle newspaper in Bulawayo.

As aid groups scale back their operations, Zimbabweans are left increasingly vulnerable.

In Bulawayo, the nation's second-largest city, some residents eke out a living smuggling in goods from South Africa or Botswana to sell on street corners or in flea markets. Others stay with their parents, grandparents or cousins, one of whom might have a steady job.

In the townships and rural areas, where poverty is more severe, people are skipping meals to protect their stocks of cornmeal, which figures show have more than quintupled in price since April. Overall, the annual inflation rate is nearly 400 percent, according to government figures.

Cornmeal is central to life throughout the country. It is typically boiled into sadza, a stiff, sticky mush that often is eaten by hand. Prosperous Zimbabweans have sadza as a side dish with chicken or beef. But many poorer residents eat it at nearly every meal, often with no other food.

The corn harvest, once so bountiful that Zimbabwe exported food, has fallen sharply since 2000, the year Mugabe began violent land seizures of thousands of commercial farms owned by whites. Most of the white farmers have since fled the country, and the farms have been run by the government or doled out, generally to government cronies with little expertise in agriculture.

U.N. figures show Zimbabwe produced 2.1 million metric tons of corn in 2000, but less than 500,000 in 2002.

Yields improved to 800,000 last year, and some Zimbabweans say that better rains are making for a bigger harvest this year. Corn cobs almost fill the storage bins at some farms outside Bulawayo. But many other farms throughout the country appear overgrown and untended, the fields all but reclaimed by nature.

Official government estimates are that this year's corn harvest will be nearly triple the size of last year's, which would make it the best since 1996, when the country was still considered the breadbasket of southern Africa.

Mugabe told Britain's Sky News in May that those days were returning and the need for food aid had ended. "We are not hungry. It should go to hungrier people, hungrier countries than ourselves," Mugabe said. "Why foist this food upon us? We don't want to be choked. We have enough."

Controlling the food supply has long been used as a political tactic by Mugabe's party, according to observers and human rights activists, who say that as elections approach, the governing party rewards supporters with 50-kilogram, or about 110-pound, bags of cornmeal and withholds them from opponents.

Independent news reports indicate that Mugabe's camp is buying cornmeal from neighboring countries and storing it in warehouses ahead of national parliamentary elections in March.

As the election season nears, the Christian aid group World Vision also finds itself caught in the nation's political dynamics. World Vision announced two weeks ago that it was ending its general feeding program in Zimbabwe, which at its height delivered food to 1.5 million people a month.

"The government has made it clear to all agencies . . . that they do not expect a food aid operation," said Rudo Kwaramba, the top World Vision official in the country. "One has to be wise, if I may use that term, in the prevailing socioeconomic-political environment in Zimbabwe. You try the best that you can to maintain your operations."

Instead of feeding centers open to all hungry people, the United Nations and World Vision have shifted their focus to targeted programs at schools, orphanages and medical clinics.

The government has not yet sought to curtail those efforts, and if they continue, much of the food in the Bulawayo warehouse may be distributed over the course of coming months.

One recent morning at the Deli Primary School in Umguza, a rural area about 45 miles northwest of Bulawayo, students lined up with empty bowls in their hands. Awaiting them were steaming pots of an enriched corn and soy porridge, courtesy of the United Nations.

It was nearly 11 a.m., and for most of these children, it was their first meal of the day. They sat on brown grass, not far from dried cow dung left by cattle sharing the school's field, and scooped food into their mouths in the traditional way, with two fingers.

Through such targeted programs, the United Nations still hopes to provide food to 550,000 Zimbabweans next year.

But unless the government changes its mind, the United Nations does not intend to restart the general feeding centers that once fed 10 times that number.

"The government will want to be the one giving out food," said John Makumbe, a political science professor at the University of Zimbabwe in the capital, Harare. "You have your party card, you get your food. You don't get your party card . . . you don't get your food."

Children at the Deli Primary School in Umguza, Zimbabwe, line up for a meal provided by the U.N. World Food Program, which has been forced to scale back its efforts because of President Robert Mugabe's claim that aid is unnecessary.