Turning on the TV set these days is like being transported into some hideous nightmare-come-true. Across our screen comes the menacing figure of the ayatollah, his fierce features framed in black, breathing hatred and preaching holy war against "pagans" and Heathens." Nothing he says makes sense. None of the scenes of the carefully staged demonstrators shouting out their defiant slogans against the United States has any connection with reason or reality, except that reality, in this case, is the reality of madness.

Whether Ayatollah Khomieni's comtemptous, provacative words are intended as much for home consumption -- the demagogue's tactic for diverting attention from terrible internal problems -- as they are for international effect is beside the point. Clearly both he and his followers, and all the various Iranian spokesmen, "students," officials, or otherwise, are operating from a classic misreading of American attitudes and values.

"At times, Carter intimidates us with military threats," Khomeini says, "and at times with economic threats, but he himself knows that he is beating an empty drum. Carter does not have the guts to engage in a military operation, and they do not listen to him. . .

"All Carter's efforts and endeavors are aimed at his being reelected president when his term comes to an end. But he is barking up the wrong tree. He thought that if he were to frighten Iran, and if he were to say that we shall impose an economic embargo on Iran and shall damage Iran's economy, his nation would applaud him and later he would be made president. But he has understood that right now a vast section of the society, namely the Negroes, have demonstrated. Later, others shall join them, except those whom Carter regards as the world."

Implicit in those words stands the source of the greatest danger in the combustible situation that continues to command the world's nervous attention. A tragedy of mutual misunderstanding is being played out in the Middle East, but the most explosive ingredient stems from a monumental misperception about America and Americans.

If we don't know the Iranians, to say nothing of fanatical ayatollahs urging suicidal warfare, they surely don't know us.

Much has been reported about the mood of the country in recent days during the sordeal suffered by our citizens held hostage in Iran. It has not been exaggerated.

In traveling through the Midwest last week, gathering material for another story, nearly every person I met believed the United States should take the strongest action in retaliation against Iran. It has been years since such unanimity of opinion existed about a major issue. If the people I spoke to were in any way represtative, they overwhelmingly would favor employing American military force.

"How dare they do this to our country?" was the remark of one young woman in Ohio who expressed a common view.

After the inital bursts of emotion, the people have been notably restrained so far in expressing their anger. Yet no one should misjudge their present surface calmness for lack of will to take punishing steps against Iran. To believe that would be as wrong as the earlier misreadings about America being a paper tiger in the pre-Vietnam days.

But that kind of misunderstanding is almost matched by our own misconceptions about the realities of the shah's regime in Iran and the forces allied against him.

For instance, consider these judgments about Iranian nationalism from a scholar:

"By February . . . the shah had once again begun moving along the road toward totalitarianism," Richard W. Cottam writes. "But this was a dangerous period for him. He had failed in his effort to project the 'postive nationalist' image from the middle sector, and there was certain to be considerable time lag before his reform program could produce sustained support from the peasantry. Therefore, he had to rely on the security forces and chaqu keshan leaders as his chief instruments of control.

"Resistance quickly developed. The nationalists inside Iran were effectively controlled but the Iranian student organization represting 25,000 students in the United States and Europe, always hositle to the shah, moved into vigouous opposition. In Fars a rebellion of unknown size and duration broke out. . . . The primary opposition, however, came from religious leaders. . . The two-day rioting was led by Ayatollah Ruhollah Khomeini. . . "

That was written not yesterday but in the early 1960s. The author forecast, with remarkalbe clarity, the ultimate outcome: "almost certainly any successor regime to that dominated by the shah would make nationalism a central rallying point. . . . But a central proposition of this study is that these newly awakened Iranians are unlikely to look to the liberal intellectual nationalists for leadership. They will prefer the demagogues, who will appeal to their aspirations, frustrations and hatreds.

"The paadox is that in the interest of combatting comunism the United States has been pursuing a policy of economic determinism that might well produce not a Nasser but a Castro-type leadership."

That helps explain why we're now confronted by a true believer given to mad miscalculations of his own.