Former attorney general Ramsey Clark, one of the earliest American supporters of Iran's Islamic revolution, today urged the quick release of 53 American hostages held here for seven months and offered to take the place of one of them if that would help gain freedom for all of them.

Clark, in Tehran as a guest of the Iranian government, made his emotional appeal at an "international conference on U.S. involvement in Iran." In the course of his address, he castigated American administrations of the last 27 years for supporting the deposed shah and returning him to power in 1953 through a CIA-sponsored coup.

But Clark said Iran's holding of the hostages "cannot be justified" and "is not right."

"I am so sure that I am right in this, so sure that it is imperative that the hostages be released now. It is so important to the fulfillment of the Iranian revolution, which it is damaging in a hundred ways. It is so important to the individual justice and rights of the hostages, and it is so important to peace on earth that I offer today to take the place of any hostage if that will help resolve this tragic crisis," he said.

The militant students holding the hostages, who are now reportedly scattered in 15 Iranian cities, offered no reaction tonight to Clark's proposal.

Clark's offer was not echoed by the other nine Americans attending the conference here. They had been debating such a move over the last two days, according to some reports, but rejected it as a group effort. Some said they were surprised when Clark, one of three Americans who addressed the conference, made his statement.

"Speaking for myself," said political scientist John Gerassi in his talk, "I do not want to substitute myself for a hostage. I was invited here by the government of Iran, which I support as a friend . . . I do not believe that I should abuse the invitation I have from the government by interfering in an internal question."

Later, at a press conference, none of the Americans -- who defied the U.S. government ban on travel to Iran to come here -- said they would join in Clark's offer.

"I felt absolutely convinced he was sincere," said the Rev. Paul Washington of Philadelphia, "but I personally don't know how it would help." w

While Clark's offer was not accepted by the conference, a number of delegates -- all anti-American supporters of Iran's Islamic revolution called for an end to the holding of the hostages. These included Italian Communists, a Yugoslav, and a West German.

The open support here for the release of the hostages by Iran's friends was far greater than at the Islamic foreign ministers' conference in Islamabad, Pakistan, last month. At that conference, delegates told reporters they were quietly urging Iranian diplomats to release the hostages, but they made no public appeal.

There was some speculation here today that Iranian President Abol Hassan Bani-Sadr, who has been trying to arrange the release of the hostages, staged this conference to get friends of Iran to push his point of view in a way that could reach the hard-line clerics who are supporting the keeping of the hostages.

The American delegates, all of whom said at a press conference tonight they favor the quick release of the hostages, are trying to arrange meetings with Iranian political leaders, including some of the hard-line clerics.

In his speech to the conference this afternoon, Clark made it clear that he was on the side of Iran in its lengthy battle with the United States. He praised Ayatollah Ruhollah Khomeini's Islamic revolution as "a miracle for the century," and said "the U.S. role in Iran is for me incredibly painful." He called America's April 24 attempt to rescue the hostages, "a lawless military expedition, an assault on the sovereign territory of Iran."

Clark said he supports putting the deposed shah, Mohammad Reza Pahlavi, on trial, although he did not say where and by whom the shah should be tried. He added that the shah's wealth, "ripped from the bodies and the backs of the people of Iran, should be returned."

But despite the support the United States gave to the deposed shah, Clark disputed Iran's holding the hostages, who he said were "uninvolved in the specified offenses for which you are concerned."

"Where is Allen Dulles? Where is Kermit Roosevelt? Where is Richard Helms or Henry Kissinger or Richard Nixon?" Clark asked in a reference to U.S. leaders and officials of the State Department and Central Intelligence Agency who are seen here as longtime supporters of the shah.

Clark described those men as the people really responsible for U.S. policies in Iran and said, "If you had one of them [hostage] it might be different."

But, Clark said, the 53 hostages, who include three diplomats held at the Foreign Ministry since Nov. 4, "are little people. The effect of holding these 53, though, provides an excuse for power of intervention, for powers of imperialism, a delicious excuse to war, to dominate, to intervene.

"Finally, Clark said at the impassioned conclusion to his address, "the hostages are human beings, individuals. They are the wrong people. And there are three main risks to the hostage crisis. First, intervention and violence. Second, the terrible cost to Iran in the fulfillment of its revolution. Thirs, and finally, the morality."