In seeking United Nations economic sanctions against Iran, the United States is trying to increase its pressure on that country's revolutionary leaders by striking at the stomachs and pocketbooks of the 36 million Iranian people.

The sanctions move, announced Friday by President Carter, is not grounded in any expectations that the world community realistically can be marshalled behind the sort of total trade and financial embargo that would destroy Iran's economy.

Instead, senior U.S. officials say, the aim is to produce a credit squeeze that will accelerate the import problems already besetting Iran in ways that will affect everything from the country's capacity to produce the oil on which it depends for its livelihood to its ability to provide its people with the foodstuffs that are the staples of their traditional diet.

Such pressure won't necessarily bring Iran to its knees, the officials concede. But, they contend, it will tighten the vise of unemployment, hardship and simple inconvenience in ways that could increase significantly the political division and unrest threatening Ayatollah Ruhollah Khomeini's control over the country.

The officials say there already are signs that many Iranian leaders, particularly those charged with running the economy, are well aware of this possibility and would like to ward it off by resolving the crisis over the 50 American hostages in Tehran.

Whether they will be able to convey their concern to Khomeini in ways that will make him more flexible is still a wide-open question, the U.S. officials admit. But, as one senior U.S. official says, given the Carter administration's determination to end the confrontation without resorting to force, "economic sanctions are the logical next way to go."

That's the belief in administration policy-making circles, even though U.S. officials are aware that any sanctions resolution capable of winning adoption by the U.N. Security Council almost certainly will be a loosely worded, outwardly toothless thing.

In fact, the administration fully expects any U.N. resolution to be so full of loopholes that it would literally leave to the 152 member states the right to pick and choose how they will apply sanctions. Where most countries are concerned, particularly those from the Third World and the communist bloc, Washington does not expect any significant changes in current dealings with Iran.

Still, the United States wants a resolution, however bland and innocuous it might appear, as a springboard for setting in motion a concerted squeeze agreed to by America's principal European allies during Secretary of State Cyrus R. Vance's recent trip to Europe.

The idea is to build upon and increase the disruptive effects that U.S. officials say already have been stirred by Carter's action last month in freezing more than $8 billion in Iranian government assets held by U.S. banks and their foreign subsidiaries.

According to diplomatic sources, the countries involved in the plan for joint action -- principally West Germany, Britain, France and Italy -- have agreed to help prevent Iran from finding ways around the assets freeze by putting pressure on their banks and exporting concerns not to deal with the Iranians.

When Carter ordered the assets freeze on Nov. 14, U.S. officials say, he was motivated largely by the reflexive need to prevent Iran from carrying out a threat to withdraw its funds from the U.S. banks.

But, the officials continue, it since has become apparent that the freeze has had an effect, far greater than originally anticipated, of making it difficult for Iran to obtain essential imports.

Prior to the revolution that deposed Shah Mohammad Reza Pahlavi last year, Iran had been undergoing rapid-scale change from rural underdevelopment to industrialization and urbanization. As a result, it had become heavily dependent on large amounts of imports from the industrial nations, principally the United States and secondarily, Western Europe and Japan.

Although Khomeini has declared his intention to eliminate much of this Western influence, U.S. officials contend that trade with the West cannot be turned off in a sudden abrupt spurt without subjecting the Iranian economy to severe wrenches.

"They can talk about Islamic purification of their society all they want," says one U.S. official."But there are things from the West that they can't do without if they're going to keep the country functioning.

"If they can't buy drills and rigs and other equipment for their oil fields, they can't continue to pump oil at the rate they need. If they can't buy generators, their power plants won't be able to generate electricity in many areas of the country. Things like that inevitably translate into the unemployment and dislocations that are the wellsprings of political unrest."

Before the outbreak of the hostage crisis, Iran already had started to shift much of its trading business away from the United States, but it was still tied closely to U.S. suppliers for many key imports. In the case of some commodities such as poultry feed grains, U.S. officials say, the United States is the only country capable of supplying the quantities required by Iran's important poultry industry.

Other commodities traditionally purchased from the United States, such as wheat and rice, can be obtained elsewhere. But, U. S. officials contend, even before the crisis began, Iran was finding that switching suppliers can be expensive and difficult.

During recent months, for example, Iran contracted to buy large quantities of wheat from Australia and rice from Thailand. But it had to pay Australia $20 a ton more than it had been paying for American wheat, and the Thai rice is expected to encounter considerable resistance from Iranian consumers because it is too soft to withstand the Iranian practice of soaking it in water for 24 hours before cooking.

Such problems in changing suppliers were compounded when the hostage crisis developed and Iran found itself having to seek elsewhere for virtually all the goods it formerly bought from the United States.

But, with half of its foreign exchange reserves frozen in the United States, and with its foreign and domestic problems the center of world attention, Iran is finding suppliers in other countries unwilling to sell it goods without guaranteed payment. The major international banks are unwilling to provide the trouble-ridden country with the financing for such guarantees.

The result, according to U.S. officials, has been a clearly discernible constriction of Iranian imports that is expected to become still worse in four or five weeks, when imports contracted for before the crisis and now in the pipeline have been delivered. After that, these officials maintain, Iran will face increasingly severe shortages of many essential items ranging from food grains and cooking oils to sophisticated machinery and spare parts.

However, the officials continue, there are ways for Iran to open new channels to suppliers in their countries, particularly if major multinational banks outside the United States are willing to take the risk of helping the Iranians in exchange for promises of big profits and future business. That is why Vance went to Europe to enlist the aid of America's allies in blocking Iran's ability to use any of these potential escape routes. It took considerable negotiating, but diplomatic sources say a plan has been worked out and will be ready to fall into place shortly, either under the mandate of a U.N. resolution or, if that move fails, on a more informal basis.

Specifically, European governments are expected to intercede with their respective multinational banks to take such steps as refusing new credits to Iran, slowing down the renewal of existing credits and applying banking rules with a stringency that would declare loans in default if Iran is one day late in making a payment.

Such pressure, U.S. officials believe, should quickly make Iran such a bad credit risk that foreign suppliers would be willing to sell to it only on a cash-in-advance basis. Given their oil wealth, the Iranians probably could do that for some time to come -- but only at the cost of draining their hard currency reserves at an alarming rate.

That situation, U.S. officials say, also probably would prevent Iran from fighting back by refusing to sell its oil to the West. To do so would draw the economic noose around itself even tighter by curtailing the country's foreign exchange earnings.

In an interview last week, Khomeini loftily dismissed the implications of economic pressure by asserting, "We do not pay any attention to such things." The question now is whether the United States can make the vise it is trying to clamp on the Iranian economy close hard enough for him to start paying attention.