That Moscow is playing a malevolent hand in the country's Iran crisis became indisputable when the CIA's top-secret National Intelligence Daily informed President Carter that Moscow has privately promised to "support" Iran in the event of U.S. action.

The Russians intentionally left the nature of that "support" ambiguous. As pieced together by high-level operatives in the Pentagon, the State Department and the intelligence community the Soviet objective is clear: induce Ayatollah Ruhollah Khomeini to hold the hostages long enough to entice President Carter into military reaction.

If and when that happens, the Moscow's intention may well be to offer Iran no more than political and moral support.

But no official here is certain that the Russians would be content (as one prominent authority put it to us) "to harvest the rich anti-American crop" throughout the Moslem world that would bloom with an American attack on Iran. If not content, Moscow could indeed offer military help, using a mechanized division manned by crack Farsi-speaking Soldiers long held in readiness just north of the Iranian-Soviet border.

This malevolent game, clearly the design of Soviet policy at the highest levels, may be understandable as one superpower seeks to exploit the other's vulnerabilities. But amid the shadowy power politics swirling around Iran, there seems more than simple exploitation. This looks like calculation and design.

Some three weeks after the hostages were seized, the state-controlled Iranian radio and television suddenly stopped its harsh, unremitting criticism of the Soviet Union. This propaganda shift contradicted the historic reality that the Russian giant to Iran's north has always been viewed as a potential agressor, never a friend.

Eric Rouleau, a leading Western journalist on Iran in the left-leaning Paris daily, Le Monde, Nov. 23: "Even the denunciations of the 'oppressive communist regime' of Afghanistan have stopped, as well as the hostile slogans against the Tudeh [iran's Communist Party] that masses have been shouting out."

The shift is directly traced to Sadegh Ghotbzadeh, boss of Iranian radio and television ever since he accompanied the ayatollah from Paris to Tehran last February. This is the same man who now dominates civilian political power in Tehran, as acting foreign minister under Khomeini.

The sudden pro-Moscow progpaganda switch ordered by Ghotbzadeh coincided with the Soviet offer of "support" against U.S. military intervention, delivered in Moscow by Foreign Minister Andrei Gromyko to Iranian Ambassador Mohammed Mokri.

Although Ghotbzadeh has been portrayed on some American television screen as a moderate since his surprise elevation to foreign minister, officials here otherwise. He not attend the emergency session of the U.N. Security Council, but is regarded as an author of the boycott policy.

Indeed, U.S. officials have long suspected that of all the non-religious radicals in the Iranian revolution, Ghotbzadeh is the most dangerous to the United States. He has known Marxist links and is closely associated with radical Arab liberation fronts -- including the far-left Popular Front for the Liberation of Palestine, which helped in taking over the U.S. Embassy in Tehran Nov. 4.

Thus, the ascendancy of Ghotbzadeh clearly gave new leverage to the Soviets in expoiting U.S. vulnerability in the Iranian crisis. The day before Ghotbzadeh ruled out his presence at the Dec. 1 U.N. session, Soviet delegate Oleg Troyanovsky showed the true Soviet colors: while Moscow confirmed the illegality of the embassy takeover, he told council members, the Security Council should let the Iranians speak first at the meeting.

That would establish an immediate anti-American tone for the extraordinary Security Coucil session. The accused, not the accuser, would have the run of the courtroom at the outset of the trial.

Nobody knows how far Moscow is willing to risk playing out its malevolent hand, but an example may have been set by the Kremlin's refusal to give Carter an escape hatch in the recent Cuban crisis. The prospect of similarly disdainful treatment in this far more serious Iranian crisis helps explain the anxiety that permeates the administration today.