From the wall, Ayatollah Khomeini's massive portrait would glower down with equally suspicious eyes. Under such an accusing gaze, how could I not be guilty? Marg ba Amerika - "Death to America" - would echo from loudspeakers throughout the airport's black-painted arrivals lounge. That was the old Iran.
The new Iran greeted me last week. The arrivals lounge was painted a gleaming white. The young man at immigration was clean-shaven and wanted to talk about Iran's 2-2 draw with Australia which had just put the country's team into the World Cup finals. No one asked about Israel. And why should they, when the man who clasped Yitzhak Rabin's hand on the White House lawn was due to land at the airport less than a week later? It's a fair bet that no immigration officer is going to prowl through Yasser Arafat's passport when he arrives tomorrow for the Islamic conference - nor check the identity papers of Crown Prince Hassan of Jordan, whose trips to Israel are fully reported in the Tehran press.
A sign of the times? Or just a brief fling with reality now that Mohamed Khatami - tentatively regarded as a Good Guy by the mandarins who shape United States policy in the Middle East - is President of Iran?
A trip around town told its own story. In five days, I could find only one "Down With America" on the streets of Tehran, a fading wall-painting from the old Iran which shows bombs dropping beneath a US flag. Martyrs from the revolution and the 1980-88 Iran-Iraq war loom over the boulevards. So does Palestinian Fathi Shkaki, the leader of Islamic Jihad and its suicide bombers - surely no friend of Mr Arafat - who was assassinated by the Israelis. But the old rhetoric has disappeared.
Only a few months ago, visitors to the grotty Laleh hotel - where once I watched Revolutionary Guards hurling bottles of Moet & Chandon and Iranian sardash wine into the empty swimming pool - would have to wipe their shoes on a doormat depicting the American flag. The elevators at the Laleh - in the Shah's day, it was the Intercontinental - broke down on every floor, the phones clicked mysteriously and young men would occasionally pound on my bedroom door to demand identification papers. Journalists arriving for this week's Islamic summit, however, found a rather different Laleh.
Gone is the grubby doormat; in its place lies a massive, finely-stitched Tabriz carpet of crimson flowers and green gardens. The mangy wall-to- wall Cyril Lord-style coverings have been replaced by a marble floor. Discreet posters emphasise Iran's desire for peace through Islam. The man from the Islamic Guidance ministry greeted me effusively. "See, we have everything on network over there," he said, pointing to a bank of coloured computer screens. "You can read all the papers - the New York Times, the Washington Post, the Wall Street Journal ..." Stop, stop, I cried.
Up at the Shahr, a great green-painted ornate ocean liner of a hotel in the suburbs, young men from the Iranian broadcasting service were arranging conference passes, one of the youths a Shakespeare scholar who insisted on quoting As You Like It as he handed out glossy brochures on the conference participants.
"All the world's a stage," I was informed. "Your face, my lord," I replied, "is as a book in which men may read strange things." I received a blank stare. Macbeth, it seems, didn't go down quite so well.
And then it happened, over at broadcasting headquarters - close to the white marble palace which Iran has built for the conference - where I was supposed to collect my press pass. As the frozen fog swirled around the main gate, a policeman with a stubble beard gruffly told me to go to another entrance two miles away.
There, three more cops grudgingly allowed me to visit an office incongruously housed in an exhibition centre for the Iranian ministry of agriculture. Inside were bearded civil servants, ladies in chadors and a pile of conference documents. There were dirty cups on the desks, papers on the floor, no explanations. After half an hour, I was sent to another room. More bearded men, more dirty cups. No passes, I was told. I must go to another office round the corner. A soldier barred my way. Closed, he said. The liner was turning into the Titanic; I was back in the old Iran.
At the gate, I pleaded with the Shakespeare scholar over the phone. He was very sorry. He could help no more. "It is not my fault." Five more phone calls and another address, this time in a leafy suburb of north Tehran, an hour away through the evening traffic jams. Behind a high wall I found an office of spotless hygiene where a young woman with immaculate English apologised effusively for my problems. A brand-new government Mercedes was purring at the door, waiting to whisk me to the conference centre where more polished young men promised a press pass in hours. I had returned to the new Iran.
Or had I? True, there is a new mood in Iran, a feeling that President Khatami can present the human face of revolution, where women's equality and human rights and youth are more important than punishment and suspicion and the textual literalness of divines and the after-life. But the ferocious reaction of Ayatollah Ali Khamanei, the country's Supreme Leader - the post was Khomeini's creation - to criticism of the Iranian system of theocracy, has shown how thin are the walls separating past and future.
Mr Khamenei has suggested that Ayatollah Montazeri, a supporter of President Khatami in last May's elections, should be put on trial for questioning his office of Leader. The old Iran, it seems, is indeed just an office away.