Despite the ruling clerics' increased prestige and security following the military victories against Iraq, Tehran remains a nervous, anxious city.

At first, the uneasiness is surprising since the government is no longer directly threatened by the spectacular terrorist operations that from June to November last year seemed to threaten the Islamic republic's foundations. Scores of political figures, including a prime minister and a president, were killed in the campaign blamed on the leftist Mujaheddin-e-Khalq.

In recent months, the capital has settled down instead to a daily ration of violence. Some specialists estimate that there are from five to 10 terrorist incidents every day in Tehran alone.

The telltale signs of violence are everywhere--reinforced Revolutionary Guard sentinel posts outside strategic buildings and asphalted speed bumps on many main streets to frustrate terrorist getaway cars.

But there are no reliable statistics. The government has stopped publicizing all the terrorist incidents and all the executions carried out in the name of repressing the armed opposition.

However, even the partial listing of the violence during a recent 10-day period was impressive.

In separate attacks, terrorists wounded a high-ranking Foreign Ministry official; killed the bodyguard of the chief of the central Tehran Komiteh, or parallel police authority; opened fire on the Turkish Embassy and threw grenades near the Italian mission. Antiaircraft guns opened fire one morning, frightening residents. Iranian officials later explained that a light plane had strayed without permission into the prohibited airspace near Ayatollah Ruhollah Khomeini's compound in northern Tehran.

As for executions, their numbers are as much a matter of worried conjecture for Iranians as the extent of casualties in the 19-month war against Iraqi invaders.

Despite repeated requests, the International Committee of the Red Cross has not been authorized to visit Iranian jails for nearly a year--the period corresponding to the marked increase of violence and repression that began with president Abol Hassan Bani-Sadr's ouster in June. Journalists and diplomats have been allowed to see certain prisoners, but only on a highly selective basis.

By contrast, Iran has honored scrupulously the Geneva conventions governing the more than 20,000 Iraqis captured in the war.

A measure of the widespread quandary shared by many Iranians was the government decision to free--or commute the sentences--of 15,000 civilian prisoners. Instead of reassuring the public, the decision prompted many Iranians to question the total number of people being held if that many were to be freed.

Amnesty International has estimated that more than 4,000 Iranians have been executed since the February 1979 revolution, but the Mujaheddin have said that revolutionary justice claimed twice as many victims since last June.

Everyday conversations in Tehran are studded with case histories, or ones purporting to be, of friends and relatives who were incarcerated, often routinely tortured and sometimes subjected to mock funerals.

Teen-aged girls and boys suspected of Mujaheddin sympathies have been arrested in large numbers, according to diplomats. Only weeks ago a Westerner's friend, a young woman schoolteacher, was arrested and executed after Revolutionary Guards searched her home and found books by Karl Marx, Gustave Flaubert, Jean Jacques Rousseau and Emile Zola.

Symptomatic of the repression is the growing impression that the authorities have given top priority to weeding out leftists who fought against the late shah, Mohammad Reza Pahlavi. The leftists are considered more dangerous than the moderates in light of their key role in bringing down the monarchy. Among the list of prisoners released recently have been officials of the late shah and the succeeding, short-lived government of premier Shahpour Bakhtiar.

Every day the families of prisoners meet outside an amusement park at Vanak Square in northern Tehran in hopes of arranging visits to their relatives or providing them with food. Sometimes the families are told not to bother, a code for announcing the execution of prisoners. On some occasions, the date of execution is announced. Also on some occasions, the families are allowed to recover the bodies for burial.

A rare insight into revolutionary justice was provided by the Trotskyist publication Kargar, which was banned after printing a first-person account of conditions in Evin Prison.

Trotskyist Bahram Ali Atai described his incarceration there with 80 other persons in a 20-by-20 foot cell. Half of the prisoners were members of leftist opposition organizations, he said, but "90 percent of the prisoners believed they were not involved in armed struggle" against the state.

The worst time was late afternoon, he recounted. "Usually, the executions took place at 6 or 7 p.m., and for this reason when someone was called for in the afternoon with all his belongings, all the prisoners knew he was bound to be executed."

Imprisoned for 82 days, Atai said that "once every week we would hear the sound of firing squads and the final shot, and all the prisoners became silent. And sometimes these shots totaled 50, 60 or even 70, and none of the executions were reported in the newspapers . . . . "

"What really bothered the prisoners in the prosecutor's office was the noise from those being flagellated in the prosecution room," he added. This punishment was meted out "with the aim of extracting information or confessions from the accused," he said, rather than the usual Islamic practice of using the punishment as part of a sentence once the prisoner is found guilty.

Prisoners were "reeducated" in Evin and other prisons, he said, which for this purpose were referred to as "universities" by officials.

Those who recanted, often teen-age prisoners, performed for other prisoners, singing in groups or acting in plays or disclaiming their errors and their desire to atone. Many were encouraged to volunteer for front-line service in the war and were "martyred," as dying for the Islamic republic has come to be called.