Confronted by a new, tougher phase of sanctions scheduled to take effect this weekend, government officials here have shown a studied indifference to measures that other Iranians admit privately could aggravate the country's economic problems.

When the foreign ministers of the nine European Community countries meet in Naples Saturday to decide on the next phase of sanctions against Iran, they will have nothing before them to indicate that Tehran is moving to end the six-month-old U.S. hostage crises.

Yet, behind this attitude of public unconcern, some Iranians admit that the combination of their own governmental discord and the impact of new economic curbs could take a toll on an economy already considerably weakened. This could begin to be felt in a little as three months, some analysts predict.

So far, Iran has not responded to much coaxing by its major Western trading partners on the hostage issue, putting them in the position of having to go through with sanctions that they could prefer to avoid.

Even the halfhearted nature of the measures likely to be adopted has not persuaded Iran to make the slightest gesture that the United States' allies could seize on as proof of a desire here to solve the hostage crisis.

None of the 50 hostages at the U.S. Embassy or three diplomats being held at the Foreign Ministry was released, despite rumors that the two women, or two nondiplomats or a sick man might be "favored."

A scheduled international conference that might have adopted even handed resolutions was postponed until next month. Furthermore, no date was set for the opening of parliament, which Ayatollah Ruhollah Khomeini has said should be empowered with settling the hostages issue.

Those Iranians favoring a rapid settlement of the crisis are too weak to prevail, and Iran's official policy is that sanctions are a boon in disguise, for they will force increased revolutionary self-reliance and belt-tightening.

However, Iran has moved to protect itself if the U.S. allies vote tougher sanctions than those believed under consideration.

Even Iranians who know better somehow hope the crisis will be solved before the sanctions begin to bite. Some suggested that time will arrive in about three months with the cumulative effect of higher import costs and lower oil revenues.

Iran announced yesterday, for example, that all oil purchases must be handled henceforth by banks in Austria, India, Switzerland and Sweden. They are neutral countries unlikely to freeze Iranian assets, although banking and financial services are not thought likely to be included in the Common Market sanctions.

Also believed to be excluded from the proposed sanctions banning new trade -- except for food and medicine -- are existing contracts. Italy has some $4 billion tied up in projects, and Britain sells $345 million a year worth of automobile kits made by Talbot (formerly Chrysler U.K.) for assembly here.

Yet analysts are convinced that Iran's Achilles' heel is less likely to be sanctions affecting imports than its increasing difficulty in finding customers willing to pay for oil in hard currency.

For reasons not yet fully explained, Iran last month raised its crude to a top-of-the-market $35 a barrel.

At that price, British Petroleum, Royal Dutch Shell and the Japanese stopped buying about 800,000 barrels a day. Now economic arguments will become political with the application of sanctions banning purchase of Iranian oil.

Despite notoriously inaccurate official oil statistics, analysts are convinced that Iran is exporting only 500,000 to 600,000 barrels a day. The world oil glut apparently precludes larger hard-currency sales unless Iran drops its price.

The communist and Third World countries sending representatives here to discuss oil deals are too short of currency to be interested in anything but barter on a meaningful scale, specialists are convinced.

If computed on a yearly basis, Iran's current oil export level would produce around $8.5 billion. That would be a far cry from last year's $23 billion in oil income and not enough to meet imports estimated at $12 billion, much less current government expenditues, without recourse to the printing press or highly reluctant world money markets.

Iran could dip into its estimated $7 billion in foreign reserves unaffected by the Carter administration's freeze of Iranian assets in the United States and in overseas branches of U.S. banks.

In another precautionary move in case the United States mines or blockades Iranian ports, Iran recently signed a transport facility agreement with Turkey in exchange for a slightly preferential oil contract.

Kurdish rebels, however, have hindered both the main rail and the secondary highway links with Turkey, leaving only an already overloaded truck entry port at the town of Bazargan functioning.

Despite the Soviet's proclaimed willingness to allow Iranian-bound rail shipments through its territory, no railway cars have crossed the Julfa border point for the better part of a month.

The Soviets apparently are hoping to use the rail traffic as a lever to moderate Iranian natural gas price demands when interrupted contract talks resume.

Yet, Iranian officials appear justified in claiming that, in the words of Commerce Ministry Undersecretary Shjauddi Fattahi, "tens of countries" and "hundreds of foreign firms" are standing by to help circumvent economic sanctions.

Added problems for Iran include more risk insurance, cash payments, middlemen's fees and slower deliveries.

All of these factors are expected to cause further difficulties for the Iranian economy already hobbled by more than 30 percent inflation, unemployment of its 10 million workers, and manufacturing production running at between 30 and 40 percent of capacity.

To its credit, the government is cutting outlays for luxury goods, sophisticated weapons and nuclear power plants. Third World economies, moreover, have proved surprisingly resilient, and Iran is also bouyed by its revolutionary fervor.

Iran's immediate and even medium-term concern, according to specialists, is less a much-heralded reliance on the Soviet Bloc than an increasingly crippled economy.