The agency estimates that in Darfur alone it needs to provide emergency food for around three million people daily.
The organisation, which gives food to as many as 70 million people worldwide, says it needs to buy food several months before it can get it to the hungry.
Sheeran said if extra money does not come through before May "depending how big the gap is ... it could be quite a dramatic effect" in how much aid can be delivered.
Earlier this month, Sheeran said that the high prices of food and oil have been swelling the ranks of the hungry since last summer, and cautioned that the crisis would continue for several years.
Sheeran said that a 40 per cent rise in the cost of fuel and commodities such as grain since mid-2007 have raised the cost of food and transport, causing the shortfall in the agency's 2008 budget.
She said that the shortfall as of February 25 meant the agency needs an extra $375m for food and $125m to transport it.
In the letter to donor countries, Sheeran said that WFP was trying to deal with the soaring prices by buying 80 per cent of food in local and regional markets.
"But even with our mitigation efforts, the cost of our food purchases has risen 55 per cent since June 2007," she said.
|"...even with our mitigation efforts, the cost of our food purchases has risen 55 per cent since June 2007" |
Josette Sheeran, WFP executive director
"We urge your government to act quickly on this request so that we may avoid cutting the rations for those who rely on the world to stand by them in times of abject need."
The agency said that Afghanistan was among the most vulnerable nations, where the difficulties of procuring food were aggravated by the fighting there.
It also cited recent food riots in Burkina Faso, Cameroon, Senegal and Morocco.
Sheeran said she would discuss the issue with African finance and economy ministers at a meeting next week in Addis Ababa, Ethiopia.
Switches to biofuels around the world have also exacerbated the situation.
Corn, soybeans, sugar cane and other crops are being increasingly seen as sources of clean and cheap biofuels.
This means less grain is available for human consumption, driving up prices for basic foodstuffs.
Another UN agency based in Rome, the Food and Agriculture Organisation, estimates that 100m tonnes of cereals are diverted to the production of biofuels each year.