KAMPONG SPEU, Cambodia — At dawn in a ramshackle elementary school in rural Cambodia, the children think of only one thing: their stomachs. They anxiously await the steaming buckets of free rice delivered to their desks.

But by the end of the month, they will no longer get free breakfast from the United Nations World Food Program. About 450,000 Cambodian students will become the latest victims of soaring global food prices.

Five local suppliers have defaulted on contracts to provide rice because they can get a higher price elsewhere, program officials say. Prices of rice have tripled on the global market since December.

Faced with a shortfall of more than 14,000 tons of rice, and with more pressing needs to meet, the World Food Program stopped the free breakfasts in March. The schools’ remaining stocks are expected to run out in the coming days. That will leave students without what was often the best meal they got all day.

“I feel hopeless,” a 15-year-old in sixth grade, Boeurn Srey Leak, said.

Rich countries have pledged $469 million for food aid to address what is expected to be a $755 million deficit, due to food prices that have risen 76% since December. America, already the largest provider of food aid, is expected to contribute almost a third of that money. If Congress approves, America will contribute $770 million more to be available after October 1.

But the money will not arrive in time to save some food programs from being cut or ended.

“I don’t think there is a single program that doesn’t have some kind of concerns because they have to scale down,” an official of the World Food Program which feeds almost 89 million people worldwide, including 58.8 million children, Susana Rico, said. “The majority of countries will suffer some kind of cutbacks in rations or programs in the next three to five months.”

The numbers are grim. In Burundi, Kenya, and Zambia, hundreds of thousands of people face cuts in food rations after June. In Iraq, 500,000 recipients will likely lose food aid. In Yemen, it’s 320,000 households.

Private aid agencies based in America also said food price hikes are hurting their projects.

Mercy Corps will likely distribute 20% less food to Iraqi refugees in Syria and serve 12% fewer Colombian families fleeing violence in the countryside. World Vision may stop helping 1.5 million people — nearly a quarter of the number it serves — because of rising food prices and pledged donations not yet delivered. At least a third are children.

In Cambodia, the free breakfasts that started in 2000 have made children visibly healthier, the principal of Choumpou Proek School, about 40 miles west of the capital, Phnom Penh, Nheng Vorn, said.

“They are more focused on lessons, and their reading ability has improved subsequently,” he said.

But principals at many such rural schools don’t have the money to replace the breakfast program. Girls in particular will be at risk of dropping out because families need them at home to work in the fields or help raise siblings, the World Food Program’s Cambodia director, Thomas Keusters, said. Children in Cambodia often start school late and repeat grades, he said.

“It’s not uncommon to have a girl in grade five or six who is already 15 or 16 years old,” Mr. Keusters said. “We are paying them to come to school. I’m very concerned about them because I have no rice.”