The Security Council voted 10-2 in favor of U.S.-sponsored economic sanctions against Iran tonight, but the measure was killed by a Soviet veto that Ambassador Donald F. McHenry called "a cynical and irresponsible use of veto power" whose "transparent motive" was to "curry favor with the Iranian government and people."

McHenry pledged that the United States now will apply "firmly and vigorously" its own sanctions against Iran, and urged "all members of the United Nations to join with us."

The twice-postponed vote followed an emotioal two-hour council session in which Soviet Ambassador Oleg Troyanovsky accused the United States of "deliberately acting in such a way not only to exacerbate the Iranian-American conflict," but to "increase tension" in the entire central Asian and Mediterranean region.

Voting in favor of the resolution, in addition to the United States, were Britain, France, Norway, Portugal, Tunisia, Zambia, Jamaica, Niger and the Philippines. East Germany joined the Soviets in voting against the sanctions and China, surprisingly, cast no vote. Mexico and Bangladesh abstained.

It was the second Soviet veto in a week, following Moscow's rejection of a resolution calling for withdrawal of foreign -- that is, Soviet -- troops from Afghanistan.

Tonight's coucil session was called folowing what U.S. officials described as Iran's failure to clarify a proposal submitted in writing yesterday to Secretary General Kurt Waldheim to resolve the crisis begun Nov. 4 when more than 60 Americans were seized by militants in Tehran.

In an opening statement, Waldheim said he had spoken personally with Iranian foreign Minister Sadegh Ghotbzadeh this afternoon but that "it turned out that the fundamental problem remains the same -- namely, the timing of the release of the hostages and the procedure to be followed to meet the grievances of the Iranian government. To my regret, despite all our efforts, a mutually satisfactory solution to this problem has not yet been found.

According to a text of the Iranian letter published in Tehran today, the proposal made no mention of the hostages. It repeated, in what McHenry called "curious wording," its interest in a U.N. commission to investigate Iranian claims for return of the shah and his fortune, and of U.S. involvement in Iran.

"Evan the most desperate among us," McHenry said in his statement tonight, "have had difficulty finding a clue in the letter that could encourage responsible governments to delay the vote on sanctions any longer."

While McHenry called the proposed sanctions "a temperate response to Iran's continued definace of internation law will result in its increased isolation from the world community . . .

"The failure of this council to act will confirm the belief of those in Iran who feel they can act with impunity."

Troyanovsky, in preparation of his anticipated veto, had said that it was the United States and not Iran that threatened world peace. "From the very beginning, the United States embarked on a cource of crude economic and political pressure on Iran," he said.

Washington, he went on, "continues to reject efforts aimed at bringing about a solution and considers possible proposals from the Iranian side . . . rejected out of hand."

Iran, Troyanovsky said, "has done nothing which constitutes a treat to international peace and security. Such actions have been undertaken by the United States," which he said was "trampling underfoot the rights of peoples -- today in Iran, tomorrow in regard to other sovereign states."

The Soviet statement was in many ways an echo of U.S. charges that followed the Dec. 24 Soviet invasion of Afghanistan. On Dec. 31, the Soviets had abstained in a council vote on an initial Security Council resolution on Iran that led up to tonight's call for sanctions.

In the meantime, extensive charges involving the Soviet action in Afghanistan led to what both sides have described as a return to Cold War rhetoric.

It was McHenry who first brought up the subject of Afghanistan tonight. Following the Soviet veto, he said it was "extraordinary to hear from a nation which has just sent [troops] into Afghanistan" a description of sanctions "as interference in the internal affairs of Iran."

Chinese Ambassador Chen Chu said, "At present, the application of economic sanctions against Iran may not necessarily lead to the relaxation of tension and the release of the hostages. It can also be seen from developments over the past few days that the possibility still exists for a solution to be found through patience, consultations and negotiations."

Chen said, however, that the Soviets "were trying to make cheap political capital" out of the crisis in backing Iran.

Mexico, in saying it would abstain, questioned the "timeliness of the measure proposed," which "rather than having the desired effect, might be counterproductive, strengthen the intransigence and weaken the authority of those who seek dialogue."

"Moreover, it is well known that international sanctions have been generally ineffective," the Mexican representative said.

"What might occur" following santions "would be an interference in the development of political change," said Mexican Amabassador Porfirio Mundz Ledo.

"In a few short days there may be an important change in the Iranaian political process. On Jan. 25 elections will be held and while it is not certain what this simple face will mean . . . . changes can be expected that would be the beginning of institutional normalization."

Munoz said Iran's proposal "though it seemed to be weak, must be seen as the beginning of a dialogue and not the end of one." He echoed the fear of other Third World delegations, including some who voted in favor of the resolution, that "we would be locking ourselves into a course of action from which it would be difficult to extricate ourselves."

Mexico and other delegates, he said, had "suggested in a friendly fashion" that the U.S. delegation postpone or revise the scope of the resolution" -- suggestions the U.S. apparently did not respond to.

Jamaica and Niger, while saying they would suppport the resolution, reminded the council that their own interest in sanctions against South Africa in the past had brought little response, particularly from the West.

Tunsisia voiced "serious concern over the action taken by a Moslem country, a nonaligned country . . . . Our faith in this revolution was seriously shaken by an act that was . . . a serious trangression of international convention," the ambassador said in announcing his vote in favor. i

Sir Anthony Parson, speaking for Britain, said there could be "no doubt about our conviction of the illegality of the Iranian action" or of the sympathy of the British for the Americans who "in our view exercised admirable patience and restraint in this unique and truly terrible situation."

The sanctins vetoed by the Soviet Union would have banned shipments of all good except food and medicine, curtailed any new credits or loans to Iran, called for "businesslike" action in collecting payments due and reduced Iranian diplomatic personnel abroad to the minimum.

The United States and its main trading partners have already arranged to impose similar actions against Iran despite the failure of the United Nations to act.