The United States today offered to delay its efforts to have the Security Council impose economic sanctions against Iran while U.N. Secretary General Kurt Waldheim makes another attempt to win release of the American hostages in Iran.

The move indicated that the United States presently cannot muster the nine votes required in the 15-nation council for a sanctions resolution that the Carter administration would consider as putting an acceptable degree of pressure on Iran.

As a result, the U.S. plan, whose outlines were sketched by Secretary of State Cyrus R. Vance at a formal meeting of the council tonight, appears designed to buy time for another try at winning the necessary votes by demonstrating to hesitant council members the continued recalcitrance of Iran's revolutionary leaders.

On the surface, the proposal outlined by Vance would appear to fulfill President Carter's call for moving ahead with U.N. measures against Iran by asking the council to vote for imposition of sanctions.

But Vance stopped short of calliing for the council to spell out what these sanctions should be. Instead, he coupled his appeal with a proposal for Waldheim to go to Tehran or seek some other way of negotiating with the Iranians and to report back to the council "by a specified date."

Then, Vance proposed, "if the hostages have not been released when the council meets again at the early specified date, the council will at that time adopt specific sanctions . . ."

Although he did not say what the United States thinks would be an appropriate "early date," U.S. officials revealed they were thinking in terms of one week but probably would be willing to extend it for two weeks if that proves more acceptable to a majority of council members.

Even this approach, which represents at least a temporary retreat from the U.S. campaign for immediate U.N. action against Iran, is known to be encountering considerable resistance from Third World members of the council.

For that reason, the United States did not offer a draft resolution at tonight's meeting. Instead, U.S. officials are continuing their behind-the-scenes effort to work out language that will attract the necessary votes, and sources here said it probably will take until Monday before the council is in a position to vote on an actual resolution.

Carter administration officials said tonight that the U.S. plan, if adopted by the council, would have the effect both of putting Iran's revolutionary leaders under new pressure and committing the council to imposition of specific sanctions if the Waldheim mission fails.

However, U.N. sources from other countries seemed unanimous in agreeing that the real practical effect simply would be to defer the need for the council to come to grips with the sanctions questions and not impose any real obligation for meaningful steps to be taken after the deadline expires.

The real reason, the sources explained, is that on Jan. 1 five of the council's nonpermanent seats will change hands. The new council then would be under no obligation other than to consider whether it should act on the resolution passed by the outgoing council and fill in the blanks about the specifics of sanctions.

As a result, the United States then would be back in the same position that it has been this week -- lobbying other Security Council members for nine votes or more to spell out what economic and trade boycott measure U.N. members are expected to take against Iran.

This dilemma reportedly was imposed upon the United States by the unwillingness of Third World council members to line up behind a specific sanctions resolution without at least giving Iran further time to work out its problems with the United States free of U.N. interference.

In fact, several sources here reported, the U.S. lobbying effort being led by Vance and U.S. Ambassador Donald McHenry was encountering difficulty today in getting sufficient votes for a specific deadline and for actually stating in the resolution that sanctions should be imposed in principle.

Instead, the sources continued, some countries apparently were still holding out late today for an even weaker resolution that would do little more than ask Waldheim to make another try at going to Iran or negotiating with the Iranians through other means and then reporting back to the council.

Waldheim, who has tried unsuccessfully to open a negotiating channel with Ayatollah Ruhollah Khomeini's Tehran government under the mandate of a council resolution adopted earlier this month, reportedly is very unenthusiastic about the prospect of making a new attempt unless he has much greater assurances then presently seem available about its chances for success.

Reliable sources said that at a meeting with Vance this morning Waldheim stressed that he does not want to go to Tehran unless he has assurances that he would be received by Khomeini or other members of the Islamic Revolutionary Council authorized to speak for their leader.

The proposal being circulated by the United States today represents a considerable retreat from the draft resolution that U.S. delegation members were trying out on council members earlier this week.

The draft, regarded as setting out the maximum U.S. position for bargaining purposes, called for an embargo by U.N. member nations on all Iranian exports carried in Iranian ships, except oil, and all Iranian imports except food and pharmaceuticals.