Secretary of State Edmund S. Muskie has called for a U.S.-Iranian "channel of communication" to help resolve the hostage crisis, and the immediate Iranian response, while publicly scornful, left unclear whether Iran's leaders will agree to the request.

Muskie's proposal was contained in a letter that he sent several days ago to Iran's new prime minister, Mohammed Ali Rajai. On Monday, Rajai, addressing a crowd in the holy city of Qom, read the previously secret letter and commented on it in term that alternated abuse and ridicule with cryptic refusals to reply directly to the U.S. offer.

State Department officials had said previously that Muskie sent the letter because the Iranian parliament is preparing to consider what to do with the 52 American hostages and the secretary wanted to assure Rajai of U.S. willingness to cooperate in finding a reasonable solution to the 10-month hostage crisis.

After reports of Rajai's speech began coming out of Iran yesterday, the department released the text of the letter. In it, Muskie said:

"With the death of the former shah, a chapter of Iran's history is now definitely closed. With the establishment of your government, a new chapter is opened. I believe this is the moment to take a fresh look at the problems between Iran and the United States."

He went on to reaffirm the previously stated U.S. positions that the United States has "no wish to interfere" in Iran's revolutionary process and told Rajai: "I assure you that we will show the fullest respect for your independence, your territorial integrity and for the principle of noninterference."

Referring indirectly to Iranian demands that the United States admit past interference in Iran's affairs and complicity in the shah's alleged crimes, Muskie said, "There are many difficult issues between the United States and Iran. For our part, we are willing to proceed fairly and to approach each of these issues on a basis of mutual respect and equality."

He then added: "In order to begin the process of understanding each other better, I think it would be useful to establish a regular channel of communication. I would personally prefer that this be done directly, very discreetly if you wish, between representatives of our two governments. Speaking frankly and directly is the best way of removing hostility and suspicion."

"If you would prefer," Muskie went on, "we would be pleased to deal through third parties who could transmit messages between us on a regular basis." In this connection, he suggested the Swiss and Algerian embassies, which have represented U.S. and Iranian interests since diplomatic relations were broken in April, or "other persons, either official or private."

His proposal reflected the Carter administration's view, which U.S. officials say is based on a mixture of deduction, hunch and indirect signals, that Iran's leaders may be reaching the point where they want to end the impasse over the hostages. In hopes of exploiting that possibility, the administration has been probing for weeks open lines of communication to Tehran.

However, Rajai's comments in Qom gave no real clue as to whether the U.S. effort may be on the verge of a breakthrough. The prime minister repeated past accusations that the United States is torturing Iranian students in this country, aiding neighboring Iraq in aggression against Iran and is "speeding money for sabotage inside Iran."

But, when it came to responding to Muskie's call for a communications link, Rajai answered in terms that evaded the issue by taking refuge in religious and mystical rhetoric. At one point, he said:

"Diplomatic discussions are terms used during the satanic era. This does not mean that we will not talk, but according to our beliefs, if we were sure that you had repented, we would talk."

He then went on to state "six stages of repentance" apparently enunciated by Iran's top leader, Ayatollah Ruhollah Khomeini. These ranged from "confessions" and "a decision not to repeat your sins" to eating in a way "that your body will be cleansed of all that is forbidden by religion," and Rajai concluded: "Theses are the stages of repentance that we Muslims will observe, and under these circumstances, we will be prepared to hold discussions with you."

The State Department said last night that it was studying Rajai's comments and would have nothing to say at present. Privately, department sources said his remarks were being scanned for signs of whether, under the public rhetoric, he was leaving the door open for further cautious moves toward some form of communications link.

Previously, administration officials were known to have drawn some encouragement from a reply made by the Iranian parliament last week to a plea by 185 members of Congress for release of the hostages. The Iranian response called for a U.S. congressional investigation into past American actions in Iran -- an apparent softening of earlier Iranian demands that the United States admit its "guilt" and return the shah's wealth to Iran."

In a related development, the White House has counter-attacked charges by William H. Sullivan, former U.S. ambassador in Tehran, that U.S. policy broken down during the final days of Shah Mohammad Reza Pahlavi's rule because of officials at the top levels of the Carter administration working at cross purposes.

White House press secretary Jody Powell took special aim Monday at Sullivan's charges, contained in a Foreign Policy magazine article, that most of the difficulty resulted from the intervention of Carter's national security affairs adviser, Zbigniew Brezezinski.

Powell specifically dened assertions by Sullivan that Brzezinski used the shah's ambassador here, Ardeshir Zahedi, as his own agent in Tehran and that Zahedi reported to Brzezinski daily be telephone. The spokesman said that "at most there were a couple of such conversations during the period of the Shah's departure" from Iran.

In addition, Powell continued, "Dr. Brzezinski states that he neither initiated nor instructed others to initiate any telephone calls on the prospects of a military coup in Iran, such as stated by Ambassador Sullivan."

Powell said the sensitive nature of the hostage situation prevented a full reply to Sullivan's charges at this time. But, he asserted, when the full record is revealed, "it is unlikely that anyone will emerge with quite such a halo of farsightedness as that which Ambassador Sullivan has fashioned for himself."