Tehran's representative to the United Nations yesterday proposed a compromise solution to the two-month-old hostage crisis that brought a last-minute delay in a scheduled Security Council vote on economic sanctions against Iran.

The proposal, made verbally yesterday afternoon by Iranian representative Mansour Farhang to U.N. Secretary General Kurt Waldheim, was the first substantative initiative Iran has taken toward the international body since American hostages were seized at the U.S. Embassy in Tehran Nov. 4.

It remained unclear whether the proposal was a major breakthrough that could lead to the release of the hostages, or what one high-level U.S. official said could be a tactic to delay the vote on sanctions.

"In light of all this," the official said of the new developments, "we supported the idea of this delay on the conditions the council would meet [Saturday] at 6 p.m."

Last night's abbreviated council session was to take up a U.S.-sponsored resolution calling for export and banking sanctions against Iran. The Soviet Union was expected to veto the resolution, thus efectively killing it, but the Secretary of State Cyrus Vance said yesterday that the United States then would impose unilateral sanctions until the hostages were freed.

Various Security Council representatives to whom the proposal was outlined in a private session last night differed on the contents of its terms. They agreed that it mentioned acceptance of Waldhem's offer -- made during a visit to Iran last week -- of a U.N. investigation of the rule of the deposed shah and U.S. involvement in Iran.

According to one high-ranking U.N. official, Farhang told Waldheim the hostages would be released if the Security Council "recognizes the legitimacy of the claim for the extradition of the shah and the claim for the return of (his) assets" to Iran.

Although this interpretation implies that Iran will accept only the council's recognition of its claims, rather than actual realization of its demands, others understood the proposal -- which Farhang refused to present in writing -- quite differently.

At least two other Security Council members maintained that the Iranians had not relaxed their demand for the extradition of the shah, and had been vague regarding the certainty and timing of the release of the hostages.

Another uncertainty, expressed by U.S. diplomats, was the authority for the proposal. Farhang reportedly said it came from Foreign Minister Sadegh Ghotbzadeh, with no indication whether it had been approved by Iranian religious ruler Ayatollah Ruhollah Khomeini.

"I don't believe there is anything in it," U.S. Ambassador Donald McHenry said as he left the council chamber following a brief public meeting that led to the surprise postponement. "But we have the responsibility to explore anything. I don't know what [the Iranians] are headed at."

Shortly after 9 p.m., U.S. representatives hurried from the chamber to the U.S. mission, across the street from the United Nations building, where they launched into discussions with Washington. Sources said McHenry was to meet with Waldheim at around midnight to draft a written response that would be transmitted to Ghotbzadeh immediately afterward.

The response, a high-level U.S. official said, would ask for both "specificity and authority" to be clarified in writing in the Iranian proposal. The official said it would not be enough for the proposal to say authority for it derived "from the foreign minister or the Revolutionary Council."

"To be absolutely reliable," the official said, reflecting what McHenry in the council meeting called U.S. "skepticism," "a proposal must come from Mr. Khomeini or the students or militants, or mob, or whatever" holding the hostages at the U.S. Embassy in Tehran.

"That is not to say something coming from the foreign minister or Revolutionary Council would be dismissed," the official said. But he emphasized that the proposal must contain "something worth pursuing," including the exact details of when, and under what circumstances, the hostages would be released.

"The request must come in writing, saying it is from Khomeini," the official said. "Otherwise, we vote at 6 p.m." today on the sanctions resolution.

According to other diplomats, the Iranian proposal also asked for a commission of Security Council members to visit Tehran and examine Iranian grievances against the shah.

"A number of people heard" the proposal, the U.S. official said, and if you talk with each of them, as I have, you would probably end up not knowing what it is." No U.S. representative had direct contact with Farhang on the matter, he said.

In the early days of the hostage crisis, a series of short-lived foreign ministers, and subsequently Ghotbzadeh himself, made individual proposals of compromise solutions, primarily through the Western media.

Those proposals were systematically rejected by militants holding the embassy, and presumably also by Khomeini, who is the only person whose authority the militants have said they accept.

In recent weeks, however, there has been virtually no positive movement in the situation. Waldheim's mission to Tehran, which was mandated by an earlier Security Council resolution that set a Jan. 7 deadline for consideration of the U.S.-requested sanctions, yielded no apparent progress.

Last Monday, the day of the deadline, the council met privately with Waldheim, who presented a report of his mission in which he outlined little prospect of an early solution to the crisis.

This week, the council has delayed action on the Iranian question while it considered a separate resolution condemning the Soviet Union's invasion last month of Afghanistan and calling for the withdrawal of troops from that Central Asian nation.

Last night, U.S. officials assured, was to be the final meeting on sanctions against Iran and a vote had been expected.

In a statement at the brief meeting, McHenry said the United States felt strongly that the time had come to take action against Iran under terms provided in the U.N. Charter. But "certain suggestions" had been put forward from a number of quarters and these were under consideration, he said. He did not elaborate on these suggestions.

The United States agreed to the delay, a U.S. official said later, because "we want to see if this is an effort simply to deter the Security Council from voting, or if the pressure of the vote is leading Iran to a response."

Since sanctions were first proposed by the United States, Iranian officials repeatedly have said the country could withstand any emonomic pressure and that it would not influence the hostage situation.

Yesterday, before the Iranian proposal was made at the United Nations, Oil Minister Ali Akbar Moinfar said in Tehran that Iran will cut off oil shipments to any country that observes an embargo. Iran also has threatened to try the hostages on charges of spying.

The cutoff of oil exports could seriously affect U.S. allies in Western Europe that import as much as 13 percent -- in the case Italy -- of their oil from Iran. The United States maintained, however, that European allies on the Security Council, and other Western European governments, were prepared impose sanctions along with the United States even if the council resolution failed.

Although Washington was believed to be assured of the necessity nine votes in the 15-member council, a Soviet veto was virtually assured.

Last December, when the United States first indicated it would propose economic sanctions in an effort to pressure Iran, it was believed that the Soviets would abstain in any Security Council vote, as detente was believed to be more important to the Soviet Union than friendship with Iran.

Washington's recent harsh denunciations of the Soviet invasion of Afghanistan, coupled with President Carter's call for postponement of Senate ratification of the SALT II arms limitation treaty and a U.S.-pushed NATO decision to boost nuclear arms capability in Western Europe, have made detente, at least temporarily, a dead issue.

The Soviets now appear to have little to lose with a sanctions veto, and are believed to feel they have a chance to gain Iran's friendship and consolidate their Asian grip.

Although Khomeini has shown little affection for the Soviets, and the Afghan invasion has brought them popular denunciations similar to those heaped on the United States, the impostion of sanctions by the West may make the Soviets look more appealing.

Vance said earlier yesterday that the United States could "not rule out" the possibility that it would use a naval blockade in the Persian Gulf to prevent goods from reaching Iranian ports.

Assuming that Tehran does not provide a satisfactory amplification of yesterday's proposal by the 6 p.m. council session tonight, the administration has pledged that the United States, alone or with its allies, will impose sanctions. In that case, Iran's only import route may be across the Soviet border to the north.