Enghelab (Revolution) Street, which runs past the overhanging trees and steel railings in front of Tehran University, is the physical confirmation of the anarchy that has engulfed Iran since its revolution.

It is the most visible sign that the Islamic Republic is still in the throes of revolution.

On the university side of the street, the railings are largely hidden behind posters and portraits depicting Ayatollah Ruhollah Khomeini and other religious leaders. Tables set out in a long row on the edge of the pavement are covered by relgious books, tapes of readings from the Koran and more portraits of Khomeini, "the leader of the revolution."

Just 30 yards away, on the opposite curb, the frown of Khomeini is replaced by the zealous miens of other revolutionary leaders: Lein, Marx and Trotsky. Here each day the various leftist groups set up shop to display a vast variety of books and clandestinely printed magazines and pamphlets.

It is done at considerable risk, for the activits frequently areharassed and threatened with knives. Sometimes their books and papers are ripped up by young militants sent by the local revolutionary committee.

With their offices closed, their newspaper banned and all official activity disallowed, this is the only stage that leftists groups still have in Tehran.

It has often been written that the liftists have played their cards surprisingly badly in Iran, that after their substantial role in the revolution, they have allowed the fundamentalists to wrench all power away from them -- so much so that they have now for the most part gone underground.

Superficially that seems true, and fundamentalists have been able to consolidate their own power.

But the major strategic error occured before the overthrow of the late shah, when the left accepted Khomeini as the leader of the revolution.

Since the February 1979 overthrow, however, the left, on the whole, has been able to enlarge its popular base and slowly emerge as potentially the most powerful threat to the rule of the mullahs.

Of the groups making up the Iranian left, two in particular have strengthened their position while a third has found itself largely out on a limb. Of the three, the communist Tudeh Party, formed in 1941 with the aid of Soviet occupation forces, has been the least pressured.

Still very closely linked with the Soviet Union to the north, the Tudeh Party has excellently trained, unwavering cadres, and it had made full use of the anti-American emotins during the past year. This and the party's consistant support of Khomeini have led the mullahs to look upon it leniently.

However, the Tudeh Party does not represent the major threat to the regime. Its orthodox Marxist nature and close adherence to Moscowcannot remain hidden forever behind anti-American sentiments, which already are wanting. And its following, however well-organized, has remained small.

The People's Fedayan movement, avowedly Marxist-Leninist and secular, has fared worst since the revolution. Formed in the 1960s in admiration of the guerrilla-warfare achievements of Fidal Castro, it started off as a small urban guerrilla movement engaged in spectacular, but insignificant, acts against the shah's regime. Its opposition to Khomeini -- the taking up of arms sgainst the revolutionary regime in Kurdistan, for example -- and a split in the ranks that left the majority as near to Moscow as the Tudeh Party have undermined the movement's position.

The group has lost credibility with many of its former supporters and suffered most at the hands of the Revolutionary Guards and religious judges.

The movement that has developed most successfully into a mass party has been the Mujaheddin-e-Khalq, which, like the Fedayan, was a small guerrilla group in the days of the shah.

Independent of any foreign source of inspiration (important in a country obsessed with a fear of foreign domination), its ideology a weird mixture of Islamic and socialist principles, the Mujaheddin has been able to gather support from the urban poor, the youth and from a significant part of the clergy.

Although still young and inexperienced, it is well-organized in contrast to the fundamentalists and the so-called moderates and has large quantities of arms hidden away.

It showed its potential in June when about 30,000 people came to listen to Massoud Rajavi, the movement's leader, despite threats from fundamentalist extremists and the fact that there had been no mention of the meeting in the mass media.

That the fundamentalists recognize this potential was clearly shown two weeks ago at the trial of Mohammed Reza Saadati,a promiment member of Soviet Union. Although the legal proceedings were in sharp contradiction to the Islamic constitution, the foreign press and Iranian media were allowed to attend, and the defendant was given several hours to defend himself.

The trial last several days. At the end of it Saadati was sentenced to 10 years in prison, not to death as has been usual for such acts.

While the Mujaheddin has quietly continued organizing and consolidating its position with the working class, the fundamentalists who now effectively rule Iran have seen their support diminished. The war with Iraq has highlighted the weakness of the Iranian economy and armed forces for the first time to the population, and the fundamentalists are blamed.

Unemployment is rampant -- 20 percent is a conservative estimate -- and on the increase, and inflation now is running well above 60 percent. Although the mass of the Iranian populatin has remained loyal to the Islamic movement, particularly Khomeini, and has learned to live with an unpleasant economic situation, its patience may be running out.

Discontent has been visibly increasingly in Iran lately, and many Iranians seem to be turning to the left, particularly the Mujaheddin. Its silence of the moment thus may be no more than a tacticalwaiting in the wings.