Saudi Arabian Oil Minister Sheikh Ahmed Zaki Yamani, wearing a wide grin as he bantered with the press corps yesterday, looked surprisingly relaxed for a man who had just ignited the threat of an oil price war, spread panic in financial markets and forced several nations to stare into the abyss of bankruptcy.

How long the grin and the relaxed manner will last is open to question, however, as Iran has moved quickly to exploit disenchantment among moderate oil producers with the Saudi performance at the weekend OPEC meeting and is mounting a new challenge to Saudi dominance of the cartel.

Hours earlier, Yamani's 11th-hour demands that Nigeria, Libya and Algeria effectively raise prices for their superior grade of oil had caused the crucial meeting of the Organization of Petroleum Exporting Countries to dissolve in chaos and virtually ensure that the world will soon pay less for oil.

Other OPEC ministers, who complained bitterly about being tricked by the Saudis, were stunned by Yamani's power gambit and left here deeply worried about future revenues--that in many cases were already earmarked to pay off massive debts.

"How can we be asked to raise our prices at a time when crude oil markets are depressed and will continue to deteriorate?" Yahaya Dikko, Nigeria's oil minister, asked.

Iran quickly responded to the cries of betrayal. Oil Minister Mohammed Gharazi extended his sympathy and vowed that his government "will defend these oppressed peoples."

The opportunity to play the role of fraternal protector among indebted oil producers was a welcome transformation for Iran, which has been isolated in the past as a pariah prepared to sabotage OPEC if necessary to suit the aims of Tehran's fundamentalist rulers.

Ayatollah Ruhollah Khomeini's rise to power strengthened Saudi Arabia's hand in OPEC councils as other oil producers, frightened by Iran's turmoil, turned toward Riyadh for more reassuring and stable leadership.

The latest OPEC session, however, has engendered so much antagonism to Saudi Arabia's heavy-handed tactics that Iran's strident denunciations of the "rich and decadent" Arab sheikdoms may find more willing listeners.

In the past, the Saudis have tried to shirk that image by stressing the goal of a stable oil market so that less wealthy producers could reap the benefits of steady economic growth.

The failure of this week's emergency session to fix production quotas, in order to consolidate prices, revived harsh criticism of the perceived failure of Saudi policies in guiding OPEC.

Eighteen months ago, Saudi Arabia swelled its production to 10 million barrels a day to engineer an oil glut that would slow the rapid escalation in prices that had raised the cost of a barrel of oil to $34 from $12 in less than two years. The oil surplus was magnified by the current world recession.

Other producers are likely to back Iran's charge that Saudi Arabia disrupted OPEC as oil income declines and the debt burdens of many members become more acute.

Saudi Arabia, with barely 5 million citizens and financial reserves now estimated at $170 billion, possesses more wealth than it could reasonably find ways to spend. But Nigeria has fallen into desperate financial straits that could transform into grave political trouble. Venezuela faces heavy debts created by overheated development projects during the past few years.

Iran's aggressive challenge of Saudi Arabia on oil issues has been endorsed by Libya and Algeria, which both contend that only the Persian Gulf Arab states--particularly the Saudis--can afford to bear major sacrifices.

Nonetheless, Yamani said yesterday that Saudi Arabia and its gulf Arab allies had cut production to minimal levels and could no longer find buyers for their oil because of discounts offered by some countries and the qualitative advantage enjoyed by African producers.

That plight induced the Saudis to spring their trap by demanding resolution of the price differential matter just when OPEC ministers were expressing relief that an agreement on production quotas had been reached under a ceiling of 17.5 million barrels a day.

Iran's hopes to convert such discontent into a new consensus aligned against Saudi Arabia and the Arab sheikdoms could founder because of the sheer volume of oil reserves that Riyadh can manipulate to exert its will on the world market. But even if Saudi Arabia ultimately gets its way, the resentment now felt among many OPEC members could create a serious future conflict.