LONDON - Ration cards. Genetically modified crops. The end of pile-it-high, sell-it-cheap supermarkets.

These possible solutions to the first global food crisis since World War II — which the World Food Program says already threatens 20 million of the poorest children — are complex and controversial. And they may not even solve the problem as demand continues to soar.

A "silent tsunami" of hunger is sweeping the world's most desperate nations, said Josette Sheeran, the WFP's executive director, speaking Tuesday at a London summit on the crisis.

The skyrocketing cost of food staples, stoked by rising fuel prices, unpredictable weather and demand from India and China, has already sparked sometimes violent protests across the Caribbean, Africa and Asia.

The price of rice has more than doubled in the last five weeks, she said. The World Bank estimates food prices have risen by 83 percent in three years.

"What we are seeing now is affecting more people on every continent," Sheeran told a news conference.

Hosting talks with Sheeran, lawmakers and experts, British Prime Gordon Brown said the spiraling prices threaten to plunge millions back into poverty and reverse progress on alleviating misery in the developing world.

"Tackling hunger is a moral challenge to each of us and it is also a threat to the political and economic stability of nations," Brown said.

Malaysia's embattled prime minister is already under pressure over the price increases and has launched a major rice-growing project. Indonesia's government needed to revise its annual budget to respond.

Unrest over the food crisis has led to deaths in Cameroon and Haiti, cost Haitian Prime Minister Jacques Edouard Alexis his job, and caused hungry textile workers to clash with police in Bangladesh.

Former U.N. Secretary-General Kofi Annan said more protests in other developing nations appear likely. "We are going through a very serious crisis and we are going to see lots of food strikes and demonstrations," Annan told reporters in Geneva.

At streetside restaurants in Lome, Togo, even the traditional balls of corn meal or corn dough served with vegetable soup are shrinking. Once as big as a boxer's fist, the dumplings are now the size of a tennis ball — but cost twice as much.

In Yaounde, Cameroon, civil servant Samuel Ebwelle, 51, said he fears food prices will rise further.

"We are getting to the worst period of our life," he said. "We've had to reduce the number of meals we take a day from three to two. Breakfast no longer exists on our menu."

Even if her call for $500 million in emergency funding is met, food aid programs — including work to feed 20 million poor children — will be hit this year, Sheeran said.

President Bush has released $200 million in urgent aid. Britain pledged an immediate $59.7 million on Tuesday.

Even so, school feeding projects in Kenya and Cambodia have been scaled back and food aid has been cut in half in Tajikistan, Sheeran said.

Yet while angry street protesters call for immediate action, long term solutions are likely to be slow, costly and complicated, experts warn.

And evolving diets among burgeoning middle classes in India and China will help double the demand for food — particularly grain intensive meat and dairy products — by 2030, the World Bank says.

Robert Zoellick, the bank's head, claims as many as 100 million people could be forced deeper into poverty. U.N. Secretary-General Ban Ki-moon said rising food costs threaten to cancel strides made toward the goal of cutting world poverty in half by 2015.

"Now is not too soon to be thinking about the longer-term solutions," said Alex Evans, a former adviser to Britain's Environment Secretary Hilary Benn.

He said world leaders must help increase food production, rethink their push on biofuels — which many blame for pushing up food prices — and consider anew the once taboo topic of growing genetically modified crops.

But Evans, now a visiting fellow at New York University's Center on International Cooperation, said increasing the amount of land that can be farmed in the developing world will be arduous.

"It's almost like new oil or gas fields; they'll tend to be the hardest to reach places, that need new roads and new infrastructure to be viable," he said.

The will to increase food production exists, as does most of the necessary skills, but there are major obstacles, including a lack of government investment in agriculture and — in Africa particularly — a scarcity of fertilizers, good irrigation and access to markets.

"Many African farmers are very entrepreneurial, but they simply aren't connected to markets," said Lawrence Haddad, an economist and director of Britain's Institute of Development Studies. "They find there are no chilling plants for milk and no grinding mills for coffee."

Haddad said the likely impact of food price increases should have been anticipated. "The fact no one has previously made the link between agriculture and poverty is quite incredible," he said.

Just as new land for farming is available in Russia and Brazil, new genetically modified crops resistant to drought, or which deliver additional nutrients, could be better targeted to different regions of the developing world, Evans said. "The solutions are more nuanced than we previously thought," he added.

Sheeran said developing world governments, particularly in Africa, will need to dedicate at least 10 percent of future budgets to agriculture to boost global production.

Some experts predict other countries could follow the example of Pakistan, which has revived the use of ration cards for subsidized wheat.

The production of biofuels also needs to be urgently re-examined, Brown said.

He acknowledged that Britain this month introduced targets aimed at producing 5 percent of transport fuel from biofuels by 2010, but said his government and others should review their policies.

Production of biofuel leads to the destruction of forests and takes up land available to grow crops for food.

Brown said the impact of the food crisis won't just be felt in the developing world, but also in the checkout lane of Western supermarkets. "It it is not surprising that we see our shopping bills go up," Brown said.

Many analysts, including Britain's opposition leader David Cameron, claim that people in the West will need to eat less meat — and consume, or waste, less food in general. Some expect the shift in attitudes to herald the end of supermarket giveaways and cost-cutting grocery stores that stack goods to the ceiling and sell in bulk.

Citizens in the West, China and India must realize that the meat on their plate and biofuels in their expensive cars carry a cost for those in the developing world, Evans said.

Sheeran believes many already understand the impact. "Much of the world is waking up to the fact that food does not spontaneously appear on grocery store shelves," she said.