The climbing global price of rice and other staples shows no sign of leveling off, given caps placed on exports and various supply-side squeezes. As a result, food experts predict hunger and poverty in poor nations along with a restricted supply of grains coupled with rising prices in this country.

The worldwide rice crisis lapped over into the United States this week when Costco Wholesale and Wal-Mart's Sam's Club, the two biggest warehouse retail chains, limited the amount of bulk imported rice customers can buy. Sam's Club said the restriction is due to "recent supply and demand trends."

The shortage reflects restrictions on exports by major rice producers, notably India, Vietnam and Egypt, followed on Wednesday by Brazil, causing imbalance in world markets. These nations acted to ensure adequate domestic supplies amid rising world prices for preferable varieties of long-grain rice. Drought has contributed to the shortage, as has hoarding, experts say.

By comparison, there is an abundance of medium- and short-grain rice planted in California, the nation's second-largest rice-producing state after Arkansas. California growers will harvest approximately 4 billion pounds this year, with 40 percent of the crop to be exported, the majority to Japan. California's product, consistently among the state's top 20 crops, is known as sticky rice and is used in sushi, paella, risotto, sake, beer, baby food, rice milk and pet food.

Globally, the rice shortage occurring amid sharply rising food prices across the board is having enormous consequences, as rice provides more than one-fifth of all calories humans consume. The shortage has led to food riots around the world, including deaths in Cameroon. Protesters chanting "We're hungry!" caused Haiti to remove its prime minister.

"You are seeing the return of the food riot, one of the oldest forms of collective action," said Raj Patel, a food policy specialist and visiting scholar at the UC Berkeley Center for African Studies. He noted that the Roman statesman Cicero was once chased from his house because he had food and the intruders didn't.

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"And that happens because people do not have access to food at prices they can afford," Patel said. "That is why they take to the streets."

In London this week, the executive director of the World Food Program, Josette Sheeran, warned that more than 100 million people will be pushed into poverty by a "silent tsunami" of sharply rising food prices.

"This is the new face of hunger - the millions of people who were not in the urgent hunger category six months ago but now are," Sheeran said. "The world's misery index is rising."

In this country, the big retailers seem to be the first to curtail rice sales. Costco Wholesale said Tuesday that it is limiting quantities sold to consumers at some stores, including locations in the Bay Area. On Wednesday, Sam's Club said it is limiting the sale of Jasmine rice from Thailand and Basmati rice from India and other imported long-grain rice to four bags per member visit.

"We are working with our suppliers to address this matter to ensure we are in stock, and we are asking for our members' cooperation and patience," said Kristy Reed, a Sam's Club spokeswoman.

She said purchases of flour and oil are not restricted. The limitations on rice are on bags that are 20 pounds or larger.

Impact on restaurants

Restaurateurs are among those who buy rice at big-box retailers. Several in the Bay Area said they haven't raised menu prices despite their cost increases. Sasha Yu, an employee at Dragon River Restaurant in San Francisco, said a price increase would chase away customers. Sam Wang, an employee at Four Seasons Restaurant in San Jose, said there are no plans to boost the $1 per bowl of rice price but that could change.

Patel, the author of "Stuffed & Starved: The Hidden Battle for the World Food System," which describes a dysfunctional world food system, said he sees no reason food prices will decline. Nor does he believe consumers will cease stockpiling in anticipation that prices will continue to rise. The response is "an absolutely rational economic reason," as food is almost certain to get more expensive, said Patel.

Because of restrictions on exports, drought and uncertainty about supply, "all of a sudden you are seeing the kinds of economic behavior that are normal in a market like this," said Patel. "When people get jumpy, they start hoarding."

Patel lists five primary reasons for high food prices across the board:

-- Food production is heavily dependent on fossil fuel and oil prices are soaring.

-- As nations get richer they demand more meat, shifting grain "out of the bowls of the poorest people into the stomachs of livestock."

-- Biofuel production is boosting prices.

-- Poor harvests may be the front end of climate change.

-- Speculation on food prices fuels spikes.

Beyond the limitations on rice sales by the two large U.S. retailers, Patel said he expects the crisis to increase demand for food stamps and food aid programs in this country.

"And I think we ultimately have to come to terms with the fact that meat is going to be a lot more expensive," he said. This will lead to a shift in diet "to a more sustainable way of eating," he predicted, or at the least a "democratic conversation" about diet that is not currently taking place.

California alternative

Experts say it is possible rice consumers could switch to medium-grain rice like that grown in California as the crisis worsens, but they would have to overcome cultural loyalties - something not easily done.

Rice is planted on an estimated 549,000 acres in California, up from 534,000 acres last year, virtually all of it within 100 miles of the state Capitol and with a value to growers of about $500 million, said Tim Johnson, the president and CEO of the California Rice Commission.

Johnson said growers in the state this year will get about $20 per 100 pounds of rice, twice what they earned last year. At the same time, diesel prices have increased by more than 40 percent and fertilizer has doubled in cost, he said.

"We do not know when (the increases) will end, and we won't know until it is harvest time in October," said Johnson.

He added, "At the end of the day, the average person in California is going to buy rice for only 10 cents a serving. From an order of magnitude that is still the best deal on the plate."