A hundred days after the seizure of the hostages, a ray of hope emanates from the person of the new Iranian president, Abol Hassan Bani-Sard. But the limits on both the scope and durability of his authority remain severe. So while there is a chance he can spring the hostages soon, there is almost no possibility he can master the deeper problems of international security symptomized by the hostages.

Bani-Sadr is a 47-year-old French-trained economist who has been likened to Peter Sellers playing Inspector Clouseau. He became finance minister when Ayatollah Khomeini took over a year ago and then was acting foreign minister for a brief period after the taking of the hostages. At that time, he tried to negotiate through the United Nations a deal for their release. When word of the negotiations slipped out, he was pushed from office by more militant Islamic and Marxist figures in the Revolutionary Council around the ayatollah.

A stunning victory in the presidential election on Jan. 25 brought him back to office, and he has since taken control of the Revolutionary Council. He has revived his original hostage deal, which envisages release as part of an arrangement whereby the United States would accept an inquiry by a U.N. tribunal into the misdeeds of the shah and the role of this country in his rule.

At the moment, Bani-Sadr looks to be in relatively strong position. His assumption of the presidency coincides with the hospitalization of Ayatollah Khomeini for heart disease. So Bani-Sadr is practically the only public figure of large authority on the scene. He has shown his muscle by denouncing as "rebels" the student revolutionaries who hold the hostages, and then winning the release of a minister who had been illegally jailed.

Even that show of strength, however, is less than imperial. Moreover, the president's powers are subject to terrific erosion in the next few weeks.

The ayatollah may recover and resume his quixotic hold on affairs. Elections for a new parliament, or Majlis, are scheduled for March 7. The new Maflis is likely to be dominated by radicals Moslems still smarting from their recent encounters with Bani-Sadr. With the new Marjlis will come a new cabinet with a prime minister and other figures keen to compete against Bani-Sadr for power.

In such a competition, the odds are against the president. He is an independent in politics, unconnected with either the religious or the left-wing parties. He is actively opposed by some of the organized clergy and some of the military grouped around Adm. Ahmed Madani. He has no links with the ethnic minorities around the edges of Iran.

Presumably, what elected Bani-Sadr president was widespread hope that as an economist he would be well equipped to cope with the country's terrible problems of inflation, unemployment and food shortages. But Bani-Sadr is a weirdo among economists. He is a Paris intellectual with almost no experience in government. His views combine Islam and Marxism with bizarre results.

For example, he has abolished bank interest -- in keeping with the religious teachings about usury and the Marxist precept that value has to spring from labor. But adjusting interest rates is a critical tool of economic policy. For cultural reasons, Bani-Sadr favors economic self-sufficiency for Iran. But it is only by selling oil, and putting the proceeds into the purchase of capital good, that the Iranian economy can be revitalized. So even if the president wins the power struggle, which seems unlikely, he is apt to disappoint the hopes of his followers. All this means that the hope in Tehran is mixed with the prospect of trouble. aWith luck, the hostages may be released. But the luck will have to come soon, if it is to come at all.

Moreover, the release of the hostages will not end the chaos inside Iran. If anything, the left-wingers now satisfied with using the hostages to embarrass the United States will have to find new grievances. So the world can expect more of the conditions that have already disrupted the international oil market and have something to do with the Soviet invasion of Afghanistan and that still threaten the regimes in Turkey and Pakistan and the monarchies of the Persian Gulf, including Saudi Arabia.

The outlook, accordingly, is for increased danger in the main theater of confrontation between the great powers. The Carter administration will be under growing pressure to integrate Iran into its new strategy for the Gulf -- especially if release of the hostages removes the excuse it has so far had for doing nothing about that main source of regional trouble.