US hopes more moderate Iran will emerge from war. Economic and political pressures squeeze radicals

American officials are expressing cautious hope that Iran's declining military fortunes, combined with an apparent succession crisis and worsening economy at home, could work to strengthen the position of more moderate elements in Tehran. Reagan administration experts continue to worry that any decisive victory by Iran in its long war of attrition with Iraq would open the door to an aggressive campaign by Tehran to destabilize and topple moderate Arab governments in the Middle East.

For this reason, the US has consistently urged friendly governments not to sell arms to Iran.

[If unconfirmed reports circulating at press time are true, however, US policy with regard to sales of military equipment to Iran may have been modified. A Beirut magazine reported Monday that in exchange for Iranian help in securing the Sunday's release of David Jacobsen, an American held for 17 months by a Muslim extremist group in Lebanon, the US shipped four planeloads of spare parts for American-made warplanes and tanks purchased by Iran before the fall of Shah Muhammad Reza Pahlavi. Related story on Page 32.]

Despite the US concerns, however, a State Department official says, ``Pressures on Iran are increasing.

``If the war becomes a liability in terms of the regime's support, then you may get some recalculations about the war. Under those pressures, the influence of the [moderates] might grow,'' the official adds.

Some US government officials and private specialists were surprised when a planned Iranian offensive, designed to seize a chunk of southern Iraq probably including the Shiite Muslim city of Besra, failed to materialize in September or October. Hundreds of thousands of Iranian regulars and revolutionary guards have been mobilized along the 700-mile Iran-Iraq border since last summer waiting for the green light from Tehran.

These sources now say the delay may reflect a sober calculation by Iranian military leaders that the sustained offensive needed to seize and hold Iraqi territory could prove impossible against superior Iraqi artillery and air power.

``It would be a logistical nightmare,'' says one official, of the difficulty of keeping Iranian forces supplied with arms, ammunition, and troop reinforcements, for the most part across miles of marsh and swampland.

``Once the Iraqis regrouped [after an initial Iranian attack], they could begin pounding the supply lines,'' the official says.

``The key factor is that [the Iranians] have not been able to get the level of supplies they've really needed,'' says Middle East expert Anthony Cordesman. ``That means they're not in a position to do what they have to do - attack several points along the front and sustain a major offensive.''

Officials also point to the effect of domestic crises in sapping the momentum provided when Iranian forces seized Iraqi territory at Fao and recaptured Iran's own city of Mehran earlier this year.

The critical question of who will eventually succeed Ayatollah Ruhollah Khomeini, which presumably had been settled by Khomeini's recent designation of Ayatollah Hossein Ali Montazri, has been reopened by an outbreak of factional feuding within Iran's ruling elite. Some analysts believe the infighting may have been a central factor in Mr. Jacobsen's release.

That feuding, in turn, has been fueled by Iran's grave economic crisis and by growing political dissent. Three weeks ago a crowd of 50,000 gathered in Tehran to protest the policies of the Khomeini government.

Experts say that, given these internal pressures, the political costs of military failure could be catastrophic to the Khomeini regime. Thus, while the possibility exists that the long-awaited offensive will yet materialize, it seems clear that military decisions are now being made with caution.

What began with a border incursion into Iran by Iraqi troops in 1981 has become the longest, costliest conflict since World War II. It has been fed by what one US official calls the ``mirror-image set of miscalculations'' that Shiite Muslims in Sunni Iraq and Sunni Muslims in Shiite Iran would eventually rise in rebellion against their respective governments.

US sources say the main threat posed by an Iranian victory is not an outright military invasion of neighboring Arab states, including the vulnerable Persian Gulf sheikhdoms on the Arabian peninsula.

Instead, these sources worry that, using Lebanon as a model, Iran may seek to use military victory over Iraq as a springboard for a concerted program of subversion within other Arab states.

``What's happened in southern Lebanon is the goal of the maximalists in the Iranian regime,'' a State Department official comments. ``The intention is to undermine, then to overthrow and replace, every government in the Muslim world.'' The lesson so far in Lebanon is that the ground is fertile.

Officials here say there is little the US can do to influence the outcome of the Gulf war.