LONDON, AUG. 22 -- Slowly but surely, the United Nations embargo is beginning to hit Saddam Hussein's Iraq in a vulnerable place -- its stomach.

Reports trickling in by phone from Baghdad speak of panic buying of some foodstuffs in the capital and of the virtual disappearance of such items as cooking oil, sugar and soap. Members of the People's Guard -- the ruling Baath Party's political militia -- are reportedly going door to door in some Baghdad neighborhoods and in the Kurdistan region of northern Iraq checking freezers and storerooms, confiscating surplus stocks and arresting some residents for hoarding, a crime now punishable by death.

Many of the Iraqi soldiers occupying Kuwait appear to be ill fed and some have taken up begging or looting, in part to get enough to eat, according to witnesses there. Those fleeing Kuwait say soldiers near the Saudi border appear even more desperate for food and water.

But exiled Iraqi dissidents and analysts here warn that, despite sporadic shortages, it could take several months before the Iraqi public feels the brunt of the international sanctions. And some question whether denying food to Iraq is good policy or whether it could backfire by creating sympathy for the beleaguered regime.

Iraq is particularly vulnerable because, like many Third World nations, it cannot feed itself. Up to 75 percent of its food is imported -- a total of $2.9 billion last year. Much of it came from Western countries such as the United States, Canada and Australia, which are now in the front line of enforcing the embargo.

While Saddam must have planned his invasion of Kuwait for months, most analysts here believe he did not anticipate the harsh international response and did not stockpile large stores of food in expectation of an embargo. As a result, Iraqis, who are used to eating well, are quickly feeling the pinch.

Estimates vary widely on what Iraq does have. British intelligence reports say the country has stored four to six months' supply of grain, but is already suffering shortages of cooking oil and sugar. Where available, these commodities have doubled in price, the reports say.

U.S. Department of Agriculture estimates are even lower: two months' supply of wheat, one month of beans and barley, three months of rice, less than two weeks of corn. By careful rationing, some of these supplies could be stretched twice as long, experts say.

"Food is Saddam's Achilles' heel," said Saad Jaber, a leader of the exiled New Umma Party. "We've always said that over the centuries, Iraqis start moving when they feel it in their stomachs. This can hurt him a lot over time, but the question is whether the unity of nations will hold up long enough to make it work."

An Iraqi businessman said shortages in other essential areas are beginning to bite, such as shortage of spare parts for electric power stations, water treatment plants, phone equipment and airplanes. "Things can grind to a halt exponentially," he observed.

The confluence of the Tigris and Euphrates rivers is one of the Middle East's few potential agricultural bright spots. But two decades of Baathist central planning in agriculture -- coupled with the widespread, systematic destruction of land and water resources by Iraqi troops in war-ravaged Kurdistan, another farming center -- have wreaked profound damage to the country's food production, according to analysts here.

Production of wheat and barley fell by half between 1975 and 1987 while the country's population was doubling to its present 17 million, according to the U.N. Food and Agriculture Organization.

The 1988 cease-fire that halted the Iran-Iraq war led to rising expectations and a government effort to restock food shelves, experts say, especially in Baghdad, where about 4 million Iraqis live. The average daily intake of 3,000 calories per person is one of the highest in the Middle East.

Saddam has asked Iraqis to tighten their belts. In his Aug. 12 address, he called on Iraqi women to "accustom yourselves and the members of your families to leading a new way of life, in which the concepts of food, clothing and all your possessions and spending would be far less than what you have been accustomed to in the past."

Saddam told families to reduce by half their meat consumption and buy less rice, bread and clothes. "What is required is that nobody hoards food in his home and that he buys nothing more than what he needs actually for his daily or weekly needs because hoarding creates scarcity of food," he told them. On the following day, the Revolutionary Command Council declared that anyone who profits from hoarding food would face the death penalty.

Throughout the Iran-Iraq war, analysts say, Saddam was able to feed Iraqis thanks to financial aid from Arab neighbors such as Kuwait and to credits from the West. The United States alone supplied 2.5 million metric tons of grain, including 650,000 tons of corn, during the last year, even though Washington was winding down sales by cutting in half its credits to Iraq to $500 million.

At the time of the embargo, Iraq had contracts to buy 1.8 million tons of wheat from Australia, 94,000 tons of beef from the European Community and about $200 million of grains, beans and poultry from Turkey, according to Jonathan Crusoe, Iraq analyst at the Middle East Economic Digest. All are now in limbo, frozen by the U.N. action.

Some of the shortfall could be made up by Iraq itself. This year's domestic wheat harvest is expected to reach 400,000 tons, more than twice last year's harvest but far short of the 3.5 million tons Iraqis consume annually.

But most of the food has to be bought on the world market, and there are indicators of growing Iraqi desperation. Officials at the Jordanian Red Sea port of Aqaba last week seized a merchant ship that had been honoring the embargo and forced it to unload its cargo of sugar for Iraq, presumably under pressure from Baghdad. Crusoe cited a report from Paris that Iraqi middlemen are searching for someone to fill an order for 255,000 tons of cooking oil, virtually an entire year's supply.

"They've got three big problems," said an Arab banker who until recently helped finance grain deals for Iraq. "They can't get anyone to do the transaction. Even if they can, they can't pay for it because all of their overseas money is frozen. And even if they can pay for it, they can't ship it because of the embargo."

Exiled dissidents say the shortages and the specter of deprivation are hitting psychologically even before they hit Iraqi stomachs. "People are beginning to leave Baghdad to go where they believe there will be food," said Hoshyar Zebari of the Iraqi Kurdistan Front, one of the main underground opposition movements. "The public is in a state of fear, confused, even terrified. There is subterranean anger building up within the army officers and in the general public."

U.N. Security Council Resolution 661 exempts from the embargo food and medical supplies "in humanitarian circumstances," but U.S. officials have made it clear that they expect to control the shipment of food to keep a stranglehold on Iraq. So far, Turkey, one of Iraq's main suppliers, has gone along.

But some observers warn that a policy of deliberate hunger could backfire by increasing Iraqi solidarity while dividing the international community.

"It's more important to stop the oil from getting out than to stop food from getting in," said Selim Fakhri, a former Iraqi army colonel living here. "You don't want to be seen starving Iraq, but you want to make sure Saddam doesn't have the money to pay for food."