Kurt Waldheim does not forget Tehran. Tight-lipped and ramrod straight, he watched a macabre procession of 300 crippled and maimed Iranians, allegedly disabled by SAVAK, the shah's secret police. They waved their crutches and shouted "Death to Carter! Death to the shah!"

A 3-year-old whose arms were cut off at the shoulders by SAVAK agents, allegedly as a reprisal against his leftist father, was passed into Waldheim's arms. The boy began to cry and Waldheim, smiling wanly, handed him back to his mother, Waldheim's hands trembled as he said his "heart" was with all the people there, "whether grownups of children. You may be assured that what happened under the shah's regime will be the subject of an inquiry."

Such diplomatic assurances faded into insignificance later when a shouting, screaming mob rushed Waldheim's black Mercedes, thrusting snapshots of dead relatives at him, surrounding Waldheim with faces contorted in hatred.

"Go! Go!" commanded an aide to the driver. "Helicopter! Helicopter!" shouted the United Nations secretary general.

Without ever leaving the car to lay a wreath at the cemetery for victims of the Islamic revolution, Waldheim was whisked back to his helicopter. But not before cameras caught his white face, eyes wide in an uncharacteristic non-diplomatic frieze of terror.

Today, Waldheim -- returned from a mission of dubious distinction to try to free the hostages -- is once again cossetted in the rarefied world of the United Nations. The view from the 38th floor of the UN Building is as lofty as the aims of the UN once were. 3Manhattan twinkles in the distance, boats pass like toys far below on the East River.

It is a memorable week filled with international strife -- chaos in Tehran, Russia's invasion of Afghanistan -- but all seems smooth, hushed. Day-to-day diplomatic machinations are greased with an impenetrable layer of ritualized civility.

Six-foot-three, as thin and lean as a Giacometti statue, Waldheim folds himself into a chair amid the wood paneling and oriental rugs and the deep, tan leather sofas where he has greeted all the disparate leaders of a disparate world. The Pope. Castro. Arafat.

It is his nature -- as well as his perception of his job -- to receive them, one and all, graciously. To remain, says Waldheim, "scrupulously neutral."

"He is," says one diplomat, "an enemy of confrontation by nature."

Most of the time, most Americans regard the UN -- faded from its days of past importance -- as a harmless collection of international windbags, natering on about their special peeves. But as tanks again roll out of the Soviet Union and the threat of nuclear war is whispered anew, attention once more is riveted on the UN, its peculiar role and the forces that converge on the man who heads it.

"The secretary general is the honest broker in the game of world politics and he really has to tailor his conduct to that world. He has to quiet their fears, angers, listen to 152 nations. He really has to see all sides. It doesn't appear to be a very heroic stance very often -- and shouldn't, it you're going to do it right," says Brian Urquhart, the assistant secretary general who has worked in the UN secretariat since its inception and is commonly referred to as the "brains" of the U.N.

UN critics regard it as a useless, toothless international body. Waldheim is fond of saying he has 152 bosses, all of whom he is trying to please.

You can find every shading of opinion on who Kurt Waldheim really is and what he ought to be doing, but three major views prevail.

Waldheim, the Weakling: The adjectives of some UN observers are often biting. He has been called weak, a messenger boy, a man who lacks moral courage and an independent mind, who follows the path of least resistance.

A man who is courteous to a fault with diplomats but autocratically dismisses staff grievances and perpetuated a longtime UN practice of keeping secret dossiers on staff.

A standard put-down by some in the media is that Waldheim is the UN's "Austrian head waiter." In the cautious diplomatic world -- where ambassadors go on deep, deep, deep background and, when assured of such trust, reveal a view about as startling as the weather report -- comments are more muted. Still some murmur that Waldheim should and could be more of an activist. "His speeches are so watered down as to be meaningless," sighed one diplomat. "I suppose it would be too strong to call him spineless, but. . . ."

Waldheim, the Conciliatory General: Many diplomatic defenders contend the press doesn't understand either the role of the secretary general or the UN.

"Waldheim has been able to steer a course between the great powers and the non-aligned while helping to maintain a tolerable peace," says John Scali, a former United States ambassador to the UN. "He has sacrificed his health and many an opportunity to create a cheap headline because he genuinely believes in the goal. He has an extraordinary patience and unlimted capacity to listen to complaints, cockeyed ideas and dreams from 152 countries that no one else could tolerate."

Ivor Richard, the former UN ambassador from the United Kingdom said, "The days of Hammarskjold and his bold-initiatives diplomacy are finished. Waldheim is not an initiator but I don't know if an initiator could function in today's world. And Waldheim can be extremely touch when he has to be. In Cyprus in 1974 when it looked as if the Turks were about to fire on the UN troops, he told them to resist with all the force they could. He was commendable."

Waldheim, the Misunderstood. This is Waldheim's view of himself. He remembers every negative ever written about him and takes pains to launch an endless defense of himself and his "impossible, lonely" job.

"You have to sacrifice a lot in this job and very sincerely it saddened me that people didn't understand my approach and how hard I work to make my solution to the problems of the world, but it gives me great satisfaction to see that finally some people understand that I am not a pacifist," he says in his thickly accented English.

"That I'm not trying to avoid problems. On the contrary, I take them head on. When I asked for an emergency session of security council to deal with the Iranian problem and when I went to Hanoi and negotiated the humanitarian problems of the Cambodia crisis, all this I did on my own. See, I took indeed many important initiatives. . . ."

(Some observers argue that Waldheim takes too much credit; that in the case of Iran, for example, the United States pushed for the session.)

"I am a human being like everybody else. I'm not a piece of wood,' Waldheim continues.

"Therefore when people criticized my attitude, I certainly felt sorry about it. The one who suffered even more under this criticism was my wife. But I always told her, if you accept such a chore, you have to expect criticism. Nobody forced me to become secretary general.

"One of the most rewarding experiences," Waldheim says proudly, "was when I was able through my personal efforts to release 10 French hostages kept by an African liberation movement. . . ."

In an autobiography as yet unpublished in English, Waldheim says of such personal intervention, "Often it is best to keep silent . . . for the states concerned are rarely anxious to publicize their concessions."

A visitor mentions that it is hard to find much material on Waldheim. He says, "Ja, nobody knows and understands and nobody reads the books about me because I'm not so important." He turns to an aide.

"See, this is what I must always say. We must get this book out about me finally in English!"

"It is coming out in February," soothes the aide. Impressions

At 61, Waldheim, who is tireless, nonetheless looks tired. "He is so thin he looks like he could be a candidate for UNICEF," jokes one friend. He keeps in training of sorts, eating little at the countless banquets, drinking ginger ale or tomato juice at the countless receptions, not smoking at the countless meetings he attends.

He wears the diplomat's uniform -- three-piece dark suit, black socks and shoes, discreetly figured tie.

He is punctilious, demanding of his staff, seldom relaxes, talks in the past tense of the days when he had time to ski and swim and hike. Still, many observers feel he enjoys the perks of his $90,000-a-year post, the cosmopolitan life, and would not turn down a thrid term two years from now.

In the UN, socializing is a part of the job, and Waldheim's wife of 36 years is viewed both as an assset and tougher than Waldheim. They are considered correct, charming hosts who hit the UN circuit with awesome enthusiasm. Nine years ago, when Waldheim told a reporter how shocked she was that someone yawned through a boring speech. "It was a boring speech -- but you just can't do that!"

Today she explodes in a friendly staccato about their life. "We had planned this past weekend to be alone. You have to have some quietness, but what can you do?" The emergency session of the general assembly voting on the Afghanistan resolution and the security council meetings on economic sanctions on Iran kept her husband at the UN past midnight both Saturday and Sunday.

"I was very worried when Kurt was in Iran. I was dreadfully afraid. That child, it was dreadful. You never know who was wounded where, but missing limbs . . . that was disagreeable and terrible shocking. What brought Kurt down the most was the hatred.

"He never takes the easy way. I said, 'Kurt do you really have to go?' and he said, 'I have to go. The security council asked me to go. I know it will not be a glamorous thing, but somebody has to do it. It goes with the job.'"

As for the criticism, she says, "I get desperate -- especially when things are unjust. He could have spared himself the humilitation but somebody had to open the door in Iran. You cannot forget about 50 people.

Mors Waldheim is upset about the criticism of her husband and the shah. In Iran, crowds chanted anti-Waldheim slogans and waved photographs of him kissing the hand of Princess Ashraf Pahlavi, the shah's twin sister.

Novelist Shirley Hazzard, an indefatigable critic of the UN, wrote in the New Republic, "Year after year, as 1938 right after the Anschluss because he was well known to be an Austrian patriot. Then he was let out, but we were harassed continuoulsy by the Gestapo. It was very frightening. And then one day my brother and I were called into the army. Very soon I was wounded on the east front and that probably saved my life. I couldn't walk for a long time and I was released from active service in 1941."

Six years ago Waldhelm warned about the crisis of our future; a gloomy forecast for international turmoil.

His dark world view was in part shaped by his past. He says, "Don't forget it you look back on my life there was more trouble than than nice things. In fact there was nothing but trouble. The nice thing was perhaps my marriage to my wife. She is indeed a pillar in my life. People of course now see me as secretary general in the interesting function, important, etcetera, but who knows what I went through until I reached that point?

"I was born in 1918 -- that was the end of the Austrian empire. The break-down of a powerful empire."

His father was a teacher -- "it was a rather poor family. I still can always remember my mother asking, 'Well what can we do to survive?' Because even if you had money in the years after 1918 there was nothing to eat anyway because there was no hinterland. Everything was cut off of this truncated state of Austria. My mother didn't even know whether I, the baby, would survive physically."

Then came the civil war in 1934. "I was a commuter, every morning I got up at five o'clock to take the train from our little town to Vienna to school. One day I heard shooting, terrible shooting as we approached Vienna. It was the beginning of the civil war. It was horrible for me to see my own compatriots dead in the streets." The Germans came soon after.

By the time Waldheim was 15 he had made up his mind to be a diplomat. "I wanted to help solve the world's problems. My father wanted me to be a doctor and I refused I said 'Daddy, I cannot see blood. I don't want to be a doctor.'" After Waldhelm got out of the German army he continued his studies and met his wife at that time. "After that, things went perfectly well."

Waldhelm moved through the ranks of Austria's diplomatic service, "from the very bottom" to the ambassadorship. He is known for his patient, methodical approach. "People think anyone can be a diplomat, but you have to learn of course."

He speaks prouldy of his role as foreign minister of Austria in settling an ancient feud over a German-speaking region of Italy. "There were terrorists on both sides. For 50 years it lasted. And I started quietly but with perseverance and we finally signed the agreement."

When he took over the secretary generalship in 1971 he said, "I'm glad I'm not an intellectual ball of fire. I don't think you can solve the Un's problems that way." He also prophesied, "A secretary general that is too much of an activist, won't last longer than a year."

Waldhelm has been around for nine years -- re-elected three years ago to his second term and, some observers feel, could successfully go for an unprecedented third term. His critics in Amnesty international presented documented reports of gross violations of human rights in Iran, the United Nations secretariat -- supposed custodian of rights -- courted funds from the shah, and, in return, helped him to furbish his image."

"This whole thing is ridiculous storms Mrs. Waldhelm. "The picture kissing her hand, Should he have kissed her cheek? For a European, kissing her hand was the most non-committal thing to do. If the Pahlavis presented a check to the UN why should we refuse? That was two years ago and the shah was the official representative of the country."

A UN official, noting that there would be a long line starting with the United States if past friendships with the shah were counted said "it would be quite absurd to presume that we could refuse to see any head of any delegation."

Although Waldhelm now sees a UN inquiry into the shah's regime as a conciliatory move at the time the hostages would be released, he refrains from discussing the shah. "He never said a bad word about the shah and he never will," says Waldhelm's wife. "Whatever he did was his problem." a Professional Neutrality

Waldhelm himself steers a diplomatic course when he talks of the sights he saw in Iran. "It was a very shocking experience. It was moving. I have children and therefore I know what it means for parents to see their children mutilated in a way I have seen. It's a terrible impression. What I thought was a must make sure things of this kind do not happen -- wherever it may be -- because unfortunately that is not just limited to one country."

Above all, Waldhelm is a man who once said, "Long experience has taught me that an abrupt gesture, an ill-chosen word or an unthinking remark can prove disastrous."

He is asked if he feels President Carter made a major mistake in bringing the shah into this country. His face shows no expression. He launches into a long paragraph beginning "I think the president has handled the matter very well . . . ' Pressed to answer the initial question, Waldhelm glides into, "You see, I do not know what was behind the decision of the United States government. I really was in no way informed and therefore I cannot judge."

When observers speak of Waldhelm they often say, "Above all, he is an Austrian," meaning that he is a professional neutral. His wife is angered the most by the unsubstantiated report in Hazzard's article that Waldhelm took part in the Nazi youth movement. "That is absolutely untrue. I just see red! Kurt's family was harassed. They even had to sell their house because of the Nazis."

Waldhelm is very sensitive about criticism about serving in the German army. "You see I was criticized after I became secretary general. I was on one of these big networks and one of the first questions is "How is it possible you have served in the German army and are now the highest official of the worldwide organization?' And I said, 'Well, I have a very good feeling because I didn't volunteer to join. I was drafted.'

My family was persecuted by the Nazis. My father was put in prison in the UN, in fact, see such personal survival as a major goal. He only says, "I will cross that bridge when I come to it."

Waldhelm, whenever he steps down, is virtually certain to be the last of the old-world Western diplomats to head the U.N. The next secretary-general will more than likely be from a Third World country. When the non-aligned countries vote as a bloc they can control the UN. They played a crucial role in the UN general assembly's overwhelming rebuke this week of Russia's invasion of Afghanistan. While their non-binding vote will do little to push Russian troops out of Afghanistan, UN members universally say, "Do not underestimate the impact of such worldwide condemnation."

To UN detractors, much of the motion in this vast building is seen as an elaborate, insignificant chess game with little binding value; a "talking show" where men speaking every conceivable languague get together and haggle over every nuance. A world where "condemn" is changed to "deeply deplore" and thus makes a resolution acceptable to a needed majority. Diplomacy's Details

Waldheim, in his book, talks about the endless minutia.

In 1973, in Geneva, the first Arab and Israeli talks in about a quarter of a century looked as if they were going to collapse before they began. There was a fight over the alphabetical arrangement. The Egyptian delegate refused to sit next to the Israeli delegate, Abba Eban, "An extraordinary tooing and froing went on all night," writes Waldheim.

Waldheim appealed and appealed. An agreement was reach but it "hinged on Gromyko sitting next to Abba Eban. Gromyko indicated he wanted Kissinger himself to ask. After Kissinger did, a smiling Gromyko said yes he would 'in the interest of world peace.'"

When the PLO's Arafat came to the UN, arguing ensued with Arafat wanting the chair reserved for heads of state placed on the rostrum for Arafat's use. When some delegates protested, writes Waldheim, "I hit upon a compromise. The controversial chair, already entangled in microphone wires, was not to be removed, but neither was it to be occupied. Arafat refrained from sitting down and restricted himself to resting his hands on the back of the chair."

"The UN gets all the problems that are totally messed up and abandoned by everyone else," says one longtime observer. "There is a sense of insolubility once they get here. What people don't understand is how governments use this organization. This is the place where people come when they don't want to have a third world war. In 1973, Russia and America were being dragged against their will into the Middle East and the UN got out the peacekeeping force."

The U.S. ambassador to the U.N., Donald McHenry says "The UN plays five or six roles. Sometimes it is just a place to blow off steam, or a meeting place to resolve differences, a place to express moral outrage and put on political pressure, a place to write law and still at other times a place to put together a peace-keeping operation."

In such an arena, the secretary general has to make a choice, as one member said. "You can play to the gallery, but with such heroics you don't last very long. Or you can take sides like Trygve Lie and you don't last long at all.

"Everyone now looks at Dag Hammarskjold with love, but they forget how he was hated by many, how at the end the Russians weren't speaking to him. He succeeded in getting everyone mad at him," he said, referring to Hammarskjold taking the intitiative of getting the UN into the Congo's problems.

Of such actions, Waldheim has said, "It's a great mistake to force issues." The Waiting Game

But men like Urquhart call Waldheim courageous as well as decent. "Going to Iran was courageous," echoes another diplomat. "He accepted the humiliation that he knew would be an inevitable part of this trip because he felt it was part of his duties."

No matter what the rest of the world thinks, diplomats in this special UN would feel Waldheim's trip was in fact, not a failure. Several repeated that Waldheim "opened the lines of communication" with at least one faction -- however confused its powers are in that chaotic government. "Poor old Waldheim is trying laboriously to talk people down where they're prepared to fudge down the corners," said one colleague.

For days there were front-page headlines and behind-the-scenes activities. Middle-of-the-night phone calls to and from Tehran. Talks with the State Department. With McHenry. With the president. Then, nothing.

Waldheim is now working quietly, hoping there will be a break after Jan. 25 when Iran elects a president. Radical economist Abol Hassan Bani Sadr, now the favorite, has long proposed a quick decision to release or punish the hostages.

Waldheim holds out the hope that the president, elected by the Iranians, might be able to move the students. The signals change daily in that country of institutionalized anarchy. The Revolutionary Council, Waldheim's main contact, is impotent as the students play out their trump card, the hostages. The Iranian UN representative says first that Khomeini sees Waldheim is an acceptable mediator. The next day it is denied from Tehran.

But Waldheim plays his game of patience and perserverance.

Waldheim smiles. "My proverb is always, as long as people talk with each other they don't shoot at each other. As long as they are fighting each other her in the conference rooms of the United Nations with words, they don't shoot at each other on the battlefied.

"even if we don't have a solution, we continue."

The smile fades. "See," he says, "that is what most people do not understand."