Reacting to a purported series of messages from President Carter to Iranian leaders, Foreign Minister Sadegh Ghotbzadeh tonight predicted that the estimated 50 Americans held hostage by radical students would be transferred to government control "very soon."

His statement capped a day of confusion over the alleged messages, which Iranian officials characterized as alternately conciliatory and menacing.

At midday Monday in Tehran, a spokesman for President Abol Hassan Bani-Sadr dashed hopes of any decision about the hostages for the next 24 hours.

The spokesman Ali Garmarudi, said Bani-Sadr would reply to President Carter in a major speech scheduled for Tuesday.

"There will be nothing at all," he told reporters after conferring with Bani-Sadr amid unconfirmed reports that the Revolutionary Council was meeting with Ayatollah Ruhollah Khomeini to discuss the hostage issue.

In addition, it was disclosed that the governments of the nine European Common Market countries had sent identical letters to Iranian leaders urging them to release the hostages.

In Bern, the Swiss Foreign Ministry confirmed that the Swiss charge d'affaires in Tehran had transmitted a letter last week to Iranian President Abol Hassan Bani-Sadr from President Carter.

Bani-Sadr's office said he had received a second message from Carter this morning, reportedly also communicated through the Swiss charge and containing new proposals in connection with a "white paper" on the U.S. relationship with the deposed shah. The U.S. Senate Foreign Relations Committee is considering issuing such a document.

It was unclear whether the letter referred to by the Swiss was the same message published by Khomeini Saturday. Ghotbzadeh has spoken of at least one "oral" message transmitted by a trusted third party. The Swiss referred to a letter, the contents of which they said they did not know.

Bani-Sadr said he had told Carter in a reply to his message that a final decision on the U.S. hostages was up to the Iranian people. He also accused Carter of failing to understand the Iranian revolution.

Throughout the day Ghotbzadeh was the only major Iranian official willing to say a kind word about the United States following U.S. denials of the authenticity of the purported Carter message to Khomeini.

Informed sources said Ghotbzadeh invoked the alleged message to Khomeini to sway a 4 1/2-hour closed-door session of the Revolutionary Council to his plans for a hostage transfer.

Meanwhile, informed sources said the Revolutionary Council tonight approved in principle a revised proposal by former Irish foreign minister Sean MacBride to solve the hostage crisis.

In a telephone interview, Ghotbzadeh said he argued before the council that Carter had met many of Iran's conditions for settlement. But observers nonetheless suggested that it would be difficult to bring about the hostage transfer only a week after the deposed shah flew from Panama to Egypt, dashing Iranian hopes for his extradition.

Analysts doubted that Khomeini was in any mood to make such a gesture to the United States, judging by his personal decision yesterday to publish the controversial message to him that his entourage insists was sent by President Carter.

Yet another factor militating against any quick transfer of the hostages was a reported American ultimatum contained in one of Carter's messages demanding such action by Monday night on pain of U.S. economic and political reprisals, including explusion of all Iranian diplomats still in the United States.

Khomeini's pride would prevent him from accepting the transfer under these circumstances, observers suggested, for fear of encouraging Iranians to think that he had given in to the United States.

Ghotbzadeh told a news conference that "unfortunately the immediate denial, which I understand perfectly well was probably for internal consumption in the U.S., has diminished the effectiveness which this message could have on our public opinion."

"It is one thing to make an error in publishing a message," he said, "but it is totally unacceptable to deny the existence of something which is absolutely real."

Nonetheless he insisted that the net effect on the controversial publication "wasn't bad -- it's a little better than before."

Accentuating the positive, he said the message represented "virtually a defense of the American system and American ideals" by expressing U.S. readiness to admit past errors that are "already known to the world."

Starting with Khomeini's own son, Ahmad, quoting his father, all other commentators celebrated the ayatollah's decision to publish the message in keeping with a revolutionary penchant for open diplomacy rather than diplomatic confidentiality -- at least in this case. But they continued to denounce Carter.

The controversial Carter-Khomeini communication apparently passed through intermediaries acceptable to both governments before being translated from French to Persian, discussed by the Revolutionary Council last Thursday and delivered to Khomeini the next day.

President Bani-Sadr said today that the text of both Carter's message to Khomeini and to himself Wednesday was delivered "simultaneously" by the Swiss charge d'affaires.

Discussing the first two American communications, Khomeini's son contrasted what he said was a conciliatory tone used with his father with the "rudeness used in Mr. Bani-Sadr's message" to convey a carrot-and-stick diplomatic approach.

Ahmad Khomeini said the message to Bani-Sadr focused on "a question of Carter's presidency, of winning or losing the U.S. election [depending] on the release, or lack of release, of the hostages."

Informed sources said the United States had noted Bani-Sadr's March 10 undertaking to transfer the hostages within two weeks to government authority and warned that unless the transfer was immediate the administration's present forbearing policy could not last.

Bani-Sadr's office this morning said the first Carter message said that the United States 'is not at all willing to engage in pressure or limitations on Iran, but the hostages' situation as well as internal factors in the United States have put him under immense pressure and he connot ignore" them.

The proposal on the hostages by MacBride, a winner of both the Lenin and Nobel peace prizes who said he was invited here by Bani-Sadr, reportedly involved widening the terms of reference of the ill-fated United Nations investigative commission.

Henceforth it should also look into deposed shah Mohammad Reza Pahlavi's assets and their retrieval, he said, since the shah's physical return here appeared out of the question.

As under the original MacBride plan, the United States would be asked to accept the establishment of a Nuremberg-type tribunal to investigate the shah's alleged crimes.

The hostages would be released under the plan starting when the two governments agreed to its terms -- rather than as a precondition as in the original proposal.

The United States would be asked to unfreeze all Iranian government assets seized in reprisal for the embassy takeover, but only when all the hostages would be released.

Ghotbzadeh, who earlier today had insisted that MacBride was here on a private visit and charged that "international communism" was seeking to dominate the proposed tribunal's makeup, adopted a softer approach after the Revolutionary Council meeting.

He said he would want to see who was proposed to take part in such a tribunal and whether the United Nations would agree.

In the past, the U.N. Secretariat is said to have opposed such a formula for fear that many of its authoritarian member governments would see it as a dangerous precedent.