American hostages in Tehran could be freed in 48 hours if President Carter accepts the plan Iran has presented, Iranian President Abol Hassan Bani-Sadr said today in an interview with Italian state television.

Bani-Sadr's remarks paralleled separate statements elsewhere in Europe today by two senior Iranian officials and diplomatic comment here suggesting that the search for a solution to the hostage crisis had moved a step forward.

Much of the comment centered on the possibility that Iran was now seeking a formula for "intermediary phases" that could include the release of the hostages to a third party for safekeeping while a commission investigated Iran's complaints against the deposed shah and the United States.

In a news conference Wednesday night, President Carter said the United States accepted the formation of such a commission in principle.

"There is a proposal on President Carter's desk now which, if he accepts, can lead to the release of the hostages in 48 hours," Bani-Sadr said, according to a translation from the French made by United Press International in Rome.

The Iranian president did not repeat the three conditions he laid out earlier this week in interviews with French media, but they still appear to be the basis for the plan that he says has received the approval of Iran's ruler, Ayatollah Ruhollah Khomeini.

Those conditions include a confession of error for supporting the rule of the deposed shah, Mohammad Reza Pahlavi, a pledge to recognize Iran's military and economic independence and an acceptance of Iran's right to seek the return of the shah and of his fortune. But Bani-Sadr has implicitly dropped the previous demand for the shah's physical return in exchange for the hostages.

The Iranian president again made no mention of the shah or his money today, but he hinted broadly that U.S. humanitarian aid and resumption of the delivery of spare parts for Iran's large U.S.-supplied arsenal would be welcome evidence of American intentions toward Iran, and that Iran would be willing to pay for them with the dividend of a friendly foreign policy.

"For now, we are dependent on the United States," Bani-Sadr said. "We suffer from this dependence. For example, we had a flood, a real catastrophe, and we need help. We need help for the province of Khuzestan, for spare parts . . . Can we accept submission just because we depend on the Americans for spare parts?"

"If no obstacles are placed in the way of our becoming economically and militarily independent, then we can return not just to normality but actually to friendship," he continued in speaking of the United States.

Meanwhile, Iranian Foreign Minister Sadegh Ghobzadeh said during a news conference in Rome today that "as soon as the commission's work takes shape and place, the question of the hostages can be resolved accordingly."

Today's Bani Sadr interview, following one yesterday with French state radio in which he said that Khomeini has approved a package of proposals including release of the hostages, seemed to be part of an Iranian campaign to break out of diplomatic isolation by renewing ties with Western Europe.

The interviews coincided with Ghotbzadeh's European tour to Athens yesterday, Rome today and Paris this weekend.

"Bani-Sadr is advancing pawn by pawn, declaration by declaration, with enormous prudence," a French diplomat said. "We don't want to do or say anything that would complicate a situation that is complicated enough."

British government sources used almost identical language, adding that there is much sensitive material that could not be revealed to correspondents.

In Geneva, the Iranian ambassador to the United Nations, Mansour Farhang, said that Bani-Sadr is handling the negotiations personally in Tehran and that he did not expect anyone else to be brought in at that end until the time comes to work out details. Farhang, who said he is in Geneva for a session of the U.N. Human Rights Commission, insisted that his absence from New York has no significance.

It became increasingly clear, however, that the plan under discussion is one that would not involve immediate release of the hostages once a commission is formed, but would be what Ghotbzadeh called a "step by step" procedure.

One unconfirmed version of the release scenario, to which British sources lent credence, was that the hostages might be turned over to a third country or an international group for safekeeping while the U.N. commission does its work.

High French sources would not confirm that one candidate would be Algeria, as has been rumored, but they said such a plan would fit with the approach of those who have been working out a deal in which there would be what one French source called "intermediary phases -- not a simple freeing.

In another version of how the hostages would be freed, former Irish foreign minister Sean MacBride, frequently mentioned as a possible president of the commission, said in a telephone interview from Dublin that the commission could take custody of the hostages and then perhaps even release of them on bail.

MacBride, 76, a holder of the Nobel and Lenin Peace prizes, said that Waldheim has asked him whether he would be willing to serve on the commission if asked. He said that Waldheim had not asked whether he would serve as its president, however.

The Irishman made it clear that he has had detailed discussions with Waldheim about who should be on the commission and how it should work.

MacBride previously had been considered a proponent of a "Third World Nuremberg tribunal" that would try alleged crimes of the shah and the United States in Iran in the same spirit as the Nazi leaders were tried after World War II.

The context for that plan, in which release of the hostages was not specified, has centered primarily in discussions between Iran and Panama, where the shah currently is living in exile. French lawyers involved in the Panama-Iran negotiations said today that, while they had been asked to study the matter of extraditing the shah from Panama, they were not involved in the negotiations for a U.N. commission. Bertrane Valette, one of the lawyers, said in an interview with Associated Press that he believed the Iranians no longer were demanding the return of the shah in exchange for the hostages, but would deal with the Panamanian extradition issue later.

MacBride today appeared to have dropped his support for a "tribunal," and instead spoke only of a fact-finding inquiry.

MacBride said that Louis Pettiti, former president of the Paris Bar Association and head of the Swiss-based International Catholic Jurists Movement, had also been approached to be a commission member. Pettiti confirmed MacBride's statement in a telephone interview but stressed that he would serve only on an investigatory commission, not a tribunal.

Pettiti said that he expects Ghotbzadeh to be in touch with MacBride this weekend after the Iranian foreign minister arrives in Paris for talks with French Foreign Minister Jean Francois-Poncet.

MacBride said that he thinks that the U.N. commission shold be limited to five to seven members and perhaps include an American and an Iranian human-rights rigure. He said he had in mind former U.S. attorney general Ramsey Clark and a Tehran civil liberties lawyer, Abdul Karim Lahidji.

MacBride said the main concern was to ensure that the commission would have enough non-European and Moslem members. He said the countries he thought would be represented included Mexico, Peru and moslem Algeria and Bangladesh.

He said that the commission should hold hearings in Tehran but that it should have its seat in a European city -- Paris, Geneva, or the Hague.