Now, the worldwide food crisis is making many countries in this politically volatile region rethink that math.

The population of the region has more than quadrupled since 1950, to 364 million, and is expected to reach nearly 600 million by 2050. By that time, the amount of fresh water available for each person, already scarce, will be cut in half, and declining resources could inflame political tensions further.

Losing confidence in world markets, these nations are turning anew to expensive schemes to maintain their food supply.

Djibouti is growing rice in solar-powered greenhouses, fed by groundwater and cooled with seawater, in a project that produces what the World Bank economist Ruslan Yemtsov calls “probably the most expensive rice on earth.”

Several oil-rich nations, including Saudi Arabia, have started searching for farmland in fertile but politically unstable countries like Pakistan and Sudan, with the goal of growing crops to be shipped home.

“These countries have the land and the water,” said Hassan S. Sharaf Al Hussaini, an official in Bahrain’s agriculture ministry. “We have the money.”

In Egypt, where a shortage of subsidized bread led to rioting in April, government officials say they are looking into growing wheat on two million acres straddling the border with Sudan.

Economists and development experts say that nutritional self-sufficiency in this part of the world presents challenges that are not easily overcome. Saudi Arabia tapped aquifers to become self-sufficient in wheat production in the 1980s. By the early 1990s, the kingdom had become a major exporter. This year, however, the Saudis said they would phase out the program because it used too much water.

“You can bring in money and water and you can make the desert green until either the water runs out or the money,” said Elie Elhadj, a Syrian-born author who wrote his Ph.D. dissertation on the topic.

Egypt, too, has for decades dreamed of converting huge swaths of desert into lush farmland. The most ambitious of these projects is in Toshka, a Sahara Desert oasis in a scorched lunar landscape of sand and rock outcroppings.

When the Toshka farm was started in 1997, the Egyptian president, Hosni Mubarak, compared its ambitions to building the pyramids, involving roughly 500,000 acres of farmland and tens of thousands of residents. But no one has moved there, and only 30,000 acres or so have been planted.

The farm’s manager, Mohamed Nagi Mohamed, says the Sahara is perfect for farming, as long as there is plenty of fertilizer and water. For one thing, the bugs cannot handle the summer heat, so pesticides are not needed.

“You can grow anything on this land,” he said, showing off fields of alfalfa and rows of tomatoes and grapes, shielded from the sun by gauzy white netting. “It’s a very nice project, but it needs a lot of money.”

Mr. Mubarak calls his country’s growing population an “urgent” problem that has exacerbated the food crisis. The population grows about 1.7 percent annually, considerably slower than a generation ago but still fast enough that it is on pace to double by 2050.

Adding 1.3 million Egyptians each year to the 77 million squeezed into an inhabited area roughly the size of Taiwan is a daunting prospect for a country in which 20 percent of citizens already live in poverty.  One recent morning in the Cairo slum of Imbaba, people crammed in front of a weathered green bakery shack for their daily rations of subsidized bread, a pita-like loaf called baladi that sells for less than a penny, so cheap that some Egyptians feed it to their livestock.

“Most people are really suffering, but what can they do?” asked Mohamed Faruk, a 38-year-old grocery worker who moonlights as a bus inspector, as he carried nine loaves of baladi in newspaper.

Awatef Mahmud, a 53-year-old mother of five who sat on a nearby stoop waiting for her bread to cool, said higher prices had led to dietary changes for her family. “Instead of buying one kilo of meat every week, we buy a half a kilo,” she said. “People used to buy pasta to make for their kids. But now that it’s four and a half pounds,” she said, referring to the currency, “they give them bread instead.”

Economists say that rather than seeking to become self-sufficient with food, countries in this region should grow crops for which they have a competitive advantage, like produce or flowers, which do not require much water and can be exported for top dollar.

For example, Doron Ovits, a confident 39-year-old with sunglasses pushed over his forehead and a deep tan, runs a 150-acre tomato and pepper empire in the Negev Desert of Israel. His plants, grown in greenhouses with elaborate trellises and then exported to Europe, are irrigated with treated sewer water that he says is so pure he has to add minerals back. The water is pumped through drip irrigation lines covered tightly with black plastic to prevent evaporation.

A pumping station outside each greenhouse is equipped with a computer that tracks how much water and fertilizer is used; Mr. Ovits keeps tabs from his desktop computer.

“With drip irrigation, you save money. It’s more precise,” he said. “You can’t run it like a peasant, a farmer. You have to run it like a businessman.”

Israel is as obsessed with water as Mr. Ovits is. It was there, in the 1950s, that an engineer invented modern drip irrigation, which saves water and fertilizer by feeding it, drop by drop, to a plant’s roots. Since then, Israel has become the world’s leader in maximizing agricultural output per drop of water, and many believe that it serves as a viable model for other countries in the Middle East and North Africa.

Already, Tunisia has reinvigorated its agriculture sector by adopting some of the desert farming advances pioneered in Israel, and Egypt’s new desert farms now grow mostly water-sipping plants with drip irrigation.

The Israeli government strictly regulates how much water farmers can use and requires many of them to irrigate with treated sewer water, pumped to farms in purple pipes. It has also begun using a desalination plant to cleanse brackish water for irrigation.

“In the future, another 200 million cubic meters of marginal water are to be recycled, in addition to promoting the establishment of desalination plants,” Shalom Simhon, Israel’s agriculture minister, wrote via e-mail.

Still, four years of drought have created what Mr. Simhon calls “a deep water crisis,” forcing the country to cut farmers’ quotas.

Egypt, at least, has the Nile. Under a 1959 treaty, the country is entitled to a disproportionate share of the river’s water, a point that rankles some of its neighbors. It has built canals to bring Nile water to the Sinai Desert, to desert lands between Cairo and Alexandria and to the vast emptiness of Toshka.

For Saad Nassar, a top adviser in Egypt’s ministry of agriculture and land reclamation, the country has little choice but to try to make the desert bloom, even in unlikely places like Toshka, which it says will eventually succeed: all of Egypt’s farms and population are now crowded onto just 4 percent of its land.

“We don’t have the luxury of choosing this or that,” he said. “We have to work on every acre that is cultivatable.”