Former U.S. attorney general Ramsey Clark indicated tonight that he will establish and head a commission in the United States to investigate Iran's case against Washington as a first step leading to the release of the 53 American hostages.

The formation of the commission was suggested today by Iranian President Abol Hassan Bani-Sadr. Clark, one of the earliest American supporters of the Islamic revolution that overthrew the shah of Iran 17 months ago, suggested that the commission could use the Freedom of Information Act to obtain secret U.S. government documents.

Clark told the Associated Press that the proposal was of "enormous importance" and an "idea that I will pursue with full vigor."

In a 36-minute meeting with 10 Americans attending a government-sponsored conference here on U.S. imperialism in Iran, Bani-Sadr listed a series of specific steps he said the United States could take to win freedom for the hostages. The hostage issue has plagued U.S.-Iranian relations and carried the constant threat of military action that could spread beyond this country into the already turbulent Persian Gulf area.

According to Los Angeles attorney Leonard Weinglass, Bani-Sadr did not insist on the return of the shah to face trial here and the return of his wealth that Iranian authorities insist he plundered illegally from this country. Those two demands have consistently been made by the militants since they seized control of the U.S. Embassy on Nov. 4.

Bani-Sadr's suggestion today was similar to others made in the last seven months by him and Foreign Minister Sadegh Ghotbzadeh as steps that could lead to the release of the hostages. These two men, nonclerical supporters of the Iranian revolution, have been thwarted in their efforts by the hard-line Islamic clerics who have supported the embassy captors and who, some observers here say, have much of the power but none of the responsibility for running Iran.

All these efforts, including a U.N. commission, have been blocked by the militants and the clerics, who have stuck to their demand for the return of the shah and his wealth as the only price of freedom for the hostages.

The Clark commission, however, differs from previous proposals since it would be a nonofficial panel composed of jurists and attorneys and would not require permission from the United States government. The Iranians would have the satisfaction of airing their grievances fully and the Carter administration would be spared having to take part in what promises to be a long attack on U.S. policy in Iran.

Although Iranians insist the United States should release all it documents on its public and clandestine activities in Iran during the past 27 years, these are really not needed by any commission. Iranian students claim to have found documents in the U.S. Embassy and in the files of Iranian ministries showing how the United States was involved in Iranian affairs.

These documents allegedly include a top-secret message talking about American-supported plans for a military takeover of this country just after the shah fled.

Moreover, Iran's revolutionary leader, Ayatollah Ruhollah Khomeini, has given the newly elected parliament sole authority on the hostages' fate. The parliament is controlled by hard-line, clerical Islamic Republic Party, many of whose members have indicated already they favor putting the hostages on trial here before releasing them.

In any case, it appears it will take the parliament more than a month to organize and select a prime minister. Only then, probably in late July, will it begin to take up the hostage issue.

Further adding to the complicated political situation here, Islamic Republic Party leader, Ayatollah Mohammed Beheshti, today derided the international conference. The meeting was established by Bani-Sadr and is headed by Ghotbzadeh as a way to bring world attention to what they consider the longtime interference by the United States in Iran's internal affairs, including returning the shah to the throne in 1953 through a CIA-sponsored coup.

Beheshti has emerged as Bani-Sadr's main political opponent, challenging all the president's prerogatives under the new constitution. Although Bani-Sadr is considered a favorite of Khomeini, he appears to be losing most of the battle to Beheshti, which further complicates efforts to release the hostages, who have become pawns in Iran's internal political battles.

Nonetheless, Weinglass said he thought Bani-Sadr's plan was a well considered effort to end the hostage crisis and its release today was meant as a message to the United States. But some of the other Americans at the meeting said the Iranian president was merely floating ideas that could possibly help free the hostages.

Among the main points that Bani-Sadr raised as conditions for the hostages' release was a pledge by the United States not to interfere any more in Iran's internal affairs. Included in that pledge, Weinglass said, would be assurances that the United States would take no punitive action against Iran for holding the hostages.

Meanwhile, Khomeini said today that President Carter should be put on trial for threatening Iran and asserted "the superpowers will . . . not have the slightest effect on our will." The 80-year-old revolutionary leader said in a radio and television message, "We are not afraid of anything."