The United States, faced with unexpected support for Iran within the U.N. Security Council, said yesterday it will again postpone its diplomatic drive to impose an arms embargo on Tehran for its failure to comply with the council's demand for a total cease-fire in its war with Iraq.

State Department spokesman Charles E. Redman indicated that the United States, after delaying a sanctions move until after U.N. Secretary General Javier Perez de Cuellar's trip to Tehran and Baghdad, has decided to wait until Iranian President Ali Khamenei addresses the United Nations next week before pressing for sanctions.

The decision reflects an Iranian diplomatic success in persuading Perez de Cuellar -- and a majority of the U.N. council's members -- that Tehran may be interested finally in ending the seven-year war. Iranian leaders told the U.N. secretary general they would accept a de facto cease-fire while an impartial body assesses which side is responsible for the war.

Iraq rejected the proposal, however, insisting that Iran accept a comprehensive cease-fire and the entire U.N. resolution. Iraq has said it will agree to the measure if Iran will.

Perez de Cuellar returned to New York Wednesday after two days of talks in Tehran and Baghdad on the U.N.'s unanimous resolution of July 20 demanding a total cease-fire, withdrawal of troops to internationally recognized borders and a political settlement.

After hearing a report on the results of his mission, the 15-nation Security Council Thursday decided to shelve any consideration of a second follow-up resolution that would have imposed a mandatory arms embargo on Tehran for refusing to accept a comprehensive cease-fire.

Reflecting U.S. frustration with Iran's reply to the Security Council, Redman called on Khamenei to state "unequivocally and clearly his country's official unconditional acceptance and willingness to implement at once" the U.N. cease-fire resolution "in all of its parts, without conditions."

He also indicated the United States did not share the apparent assessment of a majority of other Security Council members that Iran may be interested in a cease-fire and peace talks.

Redman said the United States saw "no evidence" Perez de Cuellar was told anything during his trip to indicate that a cease-fire might be possible and noted that resumption of fighting threatens international shipping in the Persian Gulf and neighboring states once again.

Redman said that if Khamenei fails to give an unequivocal answer during his U.N. address, the United States will see "no responsible alternative" but to insist the Security Council "redouble its efforts" to force both Iran and Iraq to accept a cease-fire "without conditions."

He said the United States would move "rapidly" to impose an arms embargo but gave no specific deadline.