The virtual unanimity demostrated by Iran's wide array of political parties during the seizure of the U.S. Embassy and its diplomatic hostages last year has been achieved again, paradoxically in the opposite direction. As a result, the denouement of the tragedy that has been going on for almost a year seems imminent.

Except for one small, radical group, all of Iran's political parties, whether Moslem or Marxist, including the Tudeh Communist Party, now appear to be in favor of a settlement of the hostage issue on the conditions set by Ayatollah Ruhollah Khomeini.

The reasons of the various parties are diametrically different, but, in conversations since the opening of the parliamentary discussion of the hostage issue Sunday, it is clear that the prevailing mood of the assembly is to release the Americans if the United States meets Khomeini's conditions.

The first signs of this mood became apparent when an attempt was made at the start of the parliamentary discussion Sunday to postpone the hostage issue because of an Iraqi rocket attack that morning that reportedly killed more than a hundred Iranians in Dezful.

"I propose that the question be postponed indefinitely!" one deputy said. "It would be scandalous to discuss the fate of 52 healthy Americans while our citizens are being massacred!"

But another retorted, "Mr. Carter must not be given an additional pretext for discrediting us, and, in any case, we must follow the agenda!"

"Let us be responsible and take a decision without delay!" several deputies shouted.

There was another maneuver by the "diehards:" They insisted that any debate on the hostages should be public and not behind closed doors. Since public sessions are usually broadcast on radio and television, the hard-liners were hoping to "unmask in the eyes of the people" those among their colleagues who favor releasing the American prisoners.

The votes on these resolutions gave observers the first signs of the prevailing mood in the assembly. A majority voted against an adjournment and for a debate behind closed doors. The process of a settlement between Tehran and Washington had clearly begun, as leaks after the session were to confirm.

One swallow does not make a summer, but "liberals" such as former prime minister Mehdi Bazargan and "revolutionaries" -- for example Mohammed Montazeri, known for his implacable hostility to "U.S. imperialism" -- combined to recommend the hostages' release on the conditions set by Khomeini a few weeks ago.

On this last point the attitude adopted by the ad hoc committee on the fate of the U.S. captives is significant. Contrary to what people had expected, it did not propose any additional conditions. The committee's head, who is also parliamentary deputy speaker, Moussavi Khoini, told us with a broad smile Monday: "We would never have allowed ouselves to diviate so much as an inch from the imam's directives."

Therefore it should be concluded that there is no longer any question of asking President Carter to withdraw the radar planes recently sent to Saudi Arabia or to offer "public apologies" for the "crimes committed by the United States in Iran for more than 35 years," conditions that some Iranians had said might be added.

Many officials agree in private that Iran could not obtain any more concessions from the Americans and that the "price" offered by Carter now is much higher than any Tehran could hope after the presidential elections. Washington already has paid an added price of making public declarations condemning Iraq's aggression, asking for the withdrawal of Baghdad's forces from Iranian territory and guaranteeing the Islamic Republic's territorial integrity.

The immediate advantages Tehran could obtain from releasing the hostages are greater: the recovery of the funds frozen in U.S. banks, the lifting of the trade embargo imposed by the United States and the European Common Market, the end of Iran's international isolation -- all vital trump cards in the war effort that is now the priority for the Iranian leaders.

Aside from the tiny, radical leftist Mojaheddin-e-Khalq faction, which officially asked parliament to postpone the debate on the American hostages until after the U.S. elections, all the other political parties favor a settlement on Khomeini's conditions.

"We are not in favor of the seizure of hostages per se," Tudeh Communist Party Secretary General Nureddin Kianuri told us. "The operation which made it possible to mobilize the people against U.S. imperialism has lost its usefulness. The war formented against us by the United States is quite enough to enable us to pursue that same objective."

Khoini, who was behind the U.S. Embassy occupation as mentor of the Islamic students, was more explicit: "We have reaped all the fruits of our undertaking," he told us Sunday evening with a satisfied expression. "We defeated the attempt by the 'liberals' [for him the term is pejorative] to take control of the machinery of state; we forced Mr. Bazargan's government to resign; the tree of the revolution has grown and gained in strength; we have demonstrated both to our people and to international opinion that we have the means not only to resist but also defeat the all-powerful United States, which believed it held Iran in the palm of its hand."

Khoini, who is also chairman of the Iranian parliament's Foreign Affairs Commission, said he is determined to "dispel the illusions of the Shemiran (Tehran's most select districts) and the illusions that might be cherished abroad. The possible release of the hostages would not mean the end of our battle against the United States. This battle, which is intended to cut all ties of dependency with the United States, whether economic, cultural, military or social, is only just beginning. Some people have still failed to understand that the Islamic revolution is in its very essence anti-imperialist and that nothing will deflect it from its path."

This means that the votes cast Sunday by Bazargan and his friends are diametrically opposed in meaning to the votes cast by Khoini and his supporters.

Khoini said with irony that President Carter could have secured the hostages' release "a long time ago . . . If only he had been prepared to pay the price which he is now prepared to pay to ensure his reelection."

Khoini made no reference to a confidential message Washington reportedly sent to the Tehran government Oct. 23. I have reason to think that the U.S. government reiterated its acceptance of three of the four conditions set by Khomeini. As for the fourth -- return of the shah's fortune -- Washington is said to have committed itself to support any legal action that might be taken by Iranian authorities to the end. [State Department officials familiar with the Iranian situation said in Washington that no such message was sent to the Iranian government on or around Oct. 23.]

It remains to be seen whether the Iranian parliament will prove to be equally conciliatory, but the unknown factors have been markedly reduced in the last two days.