Austrian Chancellor Bruno Kreisky, the first head of government to visit Iran since the overthrow of the shah 15 months ago, led a high-level Socialist delegation here today on what he called a fact-finding mission.

Their visit was widely believed to be another attempt to find some formula to secure the release of 53 Americans held since November.

The visit of the three leaders, representing the Socialist International, came as the newly elected Iranian parliament that will decide the fate of the hostages received the blessing of Ayatollah Ruhollah Khomeini, the country's supreme religious and political leader, prior to its inauguration Wednesday.

In another development today, Syraian official Adib Daoudi, a member of the U.N. commission of inquiry on Iran, said after a one-hour meeting with Foreign Minister Sadegh Ghotbzadeh that the five-member panel might return to Tehran soon to complete its work.

The commission, appointed by Secretary General Kurt Waldheim, visited Iran in March to investigate Iranian grievances as part of what was thought to be a deal leading to the hostages' release. They were unable to see the hostages and have not yet issued their report.

Diplomats here speculated that the Kreisky mission and Daoudi's visit were part of new moves to restart negotiations that would make it easier for the new parliament to release the hostages.

All diplomatic moves stopped after the United States' aborted military rescue attempt on April 24, and most of the hostages are reported to have been moved from the U.S. Embassy in Tehran and dispersed to 14 cities throughout the country.

Kreisky did not come here in his capacity as chancellor of Austria but as a vice president of the Socialist International, an organization of socialist parties from 42 countries.

He was accompanied by Olof Palme, Swedish prime minister from 1969 to 1976 and leader of the opposition Swedish Social Democratic Party, and Felipe Gonzalez, head of the Spanish Socialist Workers' Party.

The three men were vague about their mission on their arrival here by chartered jet this afternoon. Kreisky said they want to open contacts between European socialist parties and the Iranian revolutionaries.

"We're highly interested to know more about Iran," Kreisky said. "As democratic socialists we want to establish better, closer relations with it."

He denied reports in European papers that the three were here to act as mediators between the United States and Iran in an effort seeking freedom for the hostages, who were taken Nov. 4 when militant Iranians seized the U.S. Embassy here.

"We are not coming as mediators. We are only coming as fact-finders. No one asked us to mediate, and mediation is only successful if both sides want it," said Kreisky.

But, he added, "we are interested in having facts about the hostages."

The three-man team ate dinner tonight with Ali Reza Nobari, head of the Central Bank, who just returned from a visit to Austria, and met later with Iranian President Abol Hassan Bani-Sadr, who said the delegation was welcome here because all three members supported the Palestinian cause.

Kreisky, who is of Jewish ancestry but not religion, has taken a strong pro-Arab stand on Middle East affairs, angering Israel by being one of the first European leaders to support the Palestine Liberation Organization.

The Austrian chancellor said he would be leaving here Monday.

Daoudi, a senior adviser to Syrian president Hafez Assad, returned here yesterday on behalf of the U.N. commission as a result of talks between Waldheim and Ghotzbadeh at the funeral in Belgrade of Yugoslavia's President Tito.

The Iranians have been pressing for issuance of the commission's report on the crimes of the shah during his rule here, but Waldheim has refused to release it because he believes that Iranian leaders failed to keep their part of the bargain.

At the Islamic foreign ministers' conference in Islamabad, Pakistan, Ghotbzadeh said the U.N. failure to release the report has impaired its credibility here, and it must be reestablished in the eyes of Iran.

He said he told Waldheim that if the commission returns here, it will not be able to discuss the hostage situation.

Daoudi said if the commission returns, it should be able to complete its work and present it report to Waldheim.

The commission's investigation was stalled when the students refused to allow its members to see the hostages. Today the students banned all meetings with the hostages.

One of the first issues to be taken up by the new parliament will be the release of the hostages. But the members are likely to be tied up with procedural and organizational matters for the first three or four weeks, so it will be mid-June at the earliest before they tackle the hostage question.

Khomeini, 80, told members of parliament today to avoid petty bickering and divisiveness and to work together for the good of the country and for Islam.