The former parliament building in central Tehran has never been busier. Once a caricature of democracy under Shah Mohammad Reza Pahlavi, it has become a caricature of what is described as Islamic justice and the scene of secret activity as the headquarters of Tehran's Central Revolutionary Komiteh, or committee, the Islamic Republic's effective police force.

The black Komiteh Mercedes came for me in the early afternoon -- doubtlessly it had formerly been used by the shah's secret police, SAVAK, on similar errands.

Thus began my introduction to the capricious world of Islamic justice, where Iranians risk being accused as traitors and foreigners are suspected of being spies.

It was gentler than for many Iranians. Among my future cell-mates was one scarred with an ugly knife wound in the side incurred during a struggle with the Islamic Revolutionary Guards at the time of his arrest.

Another bore numerous small bruises around his chest and shoulders, apparently from gun barrels jabbed into him when Revolutionary Guards arrived at his house to take him away.

Foreigners, ironically, are still privileged in postrevolutionary Iran. But in the paranoia and hysteria that has grown dramatically in the aftermath of the ill-fated U.S. hostage rescue operation in Iran, all Westerners run the risk of being detained.

For journalists without formal accreditation the risks are possibly greater and, as one who had no valid press visa, I took my chance. In the present turmoil in Iran nothing is certain, including expulsion orders to journalists, many of which have been overturned.

Although ordered to leave the country, I had hoped to obtain a reprieve, having worked as a resident journalist in Iran for the previous 20 months.

By the time of my arrest I had already made a reservation to leave within days. The Ministry of National Guidance, responsible for the foreign press, knew of this. But despite the evident reluctance of some of the administrative hierarchy, more fervent revolutionary elements felt that investigation of my activities by the Komiteh was necessary.

After a preliminary search of my apartment I was taken to Komiteh headquarters, along with a bag of assorted notes and documents assembled by suspicious Komiteh men unable to read English. "English people very good," they chorused as they drove into the well-guarded Komiteh compound.

But instead of the brief interrogation I had been led to expect, I sank into a Kafkaesque world where rules were made as time went on, of a formal hierarchy in which no one appeared to be in control, and a fanatical determination but no clear purpose.

For some of those arrested by the Komiteh it was a brief interlude of hours, or perhaps days. For the sad-faced man in the crude reception area who declined to give his name but said he had been a deputy minister of war under the shah, there was little hope that his arrest meant anything other than a period of prolonged imprisonment.

And for some, arrests have been the start of a procedure that ended before a firing squad.

Islamic justice, as defined by the Komiteh, was a strange mixture of contradictions. Charges of systematic torture and beatings have been leveled against Iran's prison authorities, most notably in the cases of political activists such as members of Iran's guerrilla organizations. But among the routine cases handled at the Komiteh there was little evidence of brutality.

Confined with at least three, and sometimes five persons, in a 9-by-12 foot area partitioned off the landing of a main staircase, there was no hardship beyond confinement itself. Relations were quite friendly between prisoners and jailers who, given money, would run errands to buy cigarettes, tins of fruit, or watermelons for the inmates. The food provided was ample, even appetizing.

But for the members of the Komiteh and Revolutionary Guards, there are no arrest or trial procedures and time has no meaning. Those arrested are left sometimes for days before being questioned -- let alone charged -- in a manner that leaves any concept of liberty meaningless.

The sense of injustice and bitterness was strong among my fellow-prisoners. The shrieks of "Savaki" and "fascist guards" from a woman being roughly taken out of the building one night drew muttered curses of sympathy.

The prisoners themselves reflected a system that is steeped in fear and suspicion of subterfuge against the present regime, combined with a blind devotion to Ayatollah Ruhollah Khomeini that ignores the war of succession already being fought out under him between Iran's clergy and politicians.

Among the prisoners was a 45-year-old building contractor from the southern city of Shiraz who had come to the capital for heart treatment but was denounced to the Komiteh as a subversive by someone in his hotel. He expected to be released, but had been incarcerated nine days when I left, while his wife and children waited fearfully in his hotel for the verdict.

Adherence to Islam was no guarantee of immunity from arrest. Among the short-stay inmates were two men who had pressed Islamic questions on a mullah speaking in their local mosque. The cleric, evidently unhappy with such a development, called in the Komiteh to take them away.

"Who is Mr. Reuter?" was the first question at the top of the four foolscap pages of notes assembled by my interrogator after hours of poring over my papers and notebooks.

"Reuter is a news agency," I was obliged to write down when my explanation of the nature of Reuter and its operation had finished. Undeterred and sticking religiously to his notes, my interrogator continued: "Why did you meet him?"

Questions ranged over why I had been in contact with those considered counterrevolutionaries, why my possessions included statements from dissident groups such as Iran's ethnic minorities, and why some of my contacts had expressed the apparently incomprehensible opinion that the present revolution had given way to a clerical dictatorship.

Handwritten notes on one of the bloodier incidents of the revolution were misconstrued as a diary entry to the effect that I had killed someone. "Who and why?" my interrogator wanted to know. An address in Britain taken from a letter dealing with income tax matters was also of consuming interest.

"You see, you leave me many puzzles," my questioner declared triumphantly when I was unable to give a detailed explanation of who lived there, and why. Although such interrogation held much that was pure farce, it was part of a system that has become a tyranny for many.

At one level it has meant six months' imprisonment but no trial for a former deputy prime minister of the postrevolutionary era charged with compromising the revolution by his contact with the United States. At another level it has meant more than a month's imprisonment for an American woman, Cynthia Dwyer, who had arrived in Iran as a journalist but is now held on suspicion of spying for the CIA.

But more importantly, it has comprised the revolution among many ordinary citizens. The majority of Iranians undoubtedly still support Ayatollah Khomeini and the revolution, but the disenchantment accumulating under the system is among many pressures that raise doubts about how long the present regime can survive.