Tehran, Iran — Officially, at least, the Iranian government is 100 percent Islamic. Under the rule of its powerful religious leader, Ayatollah Ruhollah Khomeini, it operates with the veneer of ''Islamic oneness.''
But beneath the veneer are several political figures and factions that interweave with the intricacy of a Persian carpet. Once Khomeini is no longer around to hold the threads together, the republic he founded threatens to unravel.
Already, several groups within the government - and a few parties out of power - are preparing for the struggle.
Khomeini's official heir apparent is Ayatollah Hussein Montazeri. Because of the intermixture of religion and politics in Iran's power structure, observers expect a religious leader or group of religious leaders to be the successor.''He is the fruit of my life,'' Khomeini once said about his disciple.
But in Tehran many see Ayatollah Montazeri as less intelligent and less clever than Khomeini. And observers do not believe he will have the power or the popularity to hold sway over the various factions. And so far, no other religious leader has come forward.
A vacuum at the top could intensify the struggle among the sharply divided factions.
Prime Minister Hossein Mussavi is head of the government, but he is unattached to any group and is known simply as a ''fairly good technician.'' Likewise the president, Sayed Ali Khamenei, plays a secondary role, which is in accordance with the Iranian Islamic Constitution. Mr. Khamenei has never fully recovered from an assassination attempt, which forces him to work only a few hours a day.
One man to watch is Hojatolislam Hashemi Rafsanjani - perhaps the second most powerful man in Iran after Khomeini. As speaker of the Majlis (parliament), Mr. Rafsanjani reigns over a very disparate group of representatives whose majority is said to be conservative.
But Western experts who watch the debates caution that it is very difficult to draw a political sketch of each representative. ''Several of them appear incoherent to us,'' says one expert.
Nevertheless, Rafsanjani enjoys the backing of the overwelming majority of the Majlis. He is praised by the few opposition leaders who remain and the communists as well. Says one diplomat: ''He is very skillful and knows how to flow with the tide.''
That political tide, according to observers in Tehran, flows between these groups:
* Hard-line Islamic fundamentalists. This group of government ministers, supported by wealthy merchants, strongly oppose any reform of the Iranian Islamic traditions. They hold key ministries, such as education and commerce, and several of them are members of the Hodjatieh, a fundamentalist Islamic movement.
The Hodjatieh are known for their anticommunist stand. At a recent demonstration for the second anniversary of the beginning of the Iran-Iraq war, important groups were shouting anti-Soviet slogans, an illustration of the rising power of the Hodjatieh.
The Majlis is controlled by a Council of Guardians made up of conservative religious leaders who veto all laws that are supposedly not compatible with the Koran, the sacred book of Islam.
* Progressive fundamentalists. Another group of government ministers support a limited though real nationalization of the economy. Their leaders are the ministers of Justice (Muhammad Asghari) and Heavy Industry (Behzad Nabavi). They also favor economic and political relations with communist countries.
* Moderate opposition. There remains a small but vocal opposition led by Mehdi Bazargan, the former prime minister who resigned the day after the American Embassy takeover. This group has some 25 representatives in the Majlis who relentlessly criticize the government. Their impact is limited, however.
''When we start speaking, the radio stops its live broadcast of the debate,'' says a member of the opposition who requested anonymity. ''We are not even allowed to publish our own newspaper.''
Majlis opposition members are regularly asked to resign by Massoud Rajavi, who from Paris leads the armed struggle against the regime. Says Mr. Rajavi: ''Khomeini uses their presence in the assembly to try to legitimize its regime.''
But, says an aide to Mr. Bazargan, ''we won't resign until we are forced to do so, because that is what the mullahs (religious leaders) would like us to do. Those who are now in Paris should have backed us when we were in the provisional government.''
* Communist Tudeh Party. It is the very pro-Soviet party, which operated from East Berlin when the Shah was still in power. The party claims its numbers are growing. Although the size of the secular left overall doesn't seem to have increased since the revolution, the Tudeh organization is attracting various independant Marxist movements.
''We support Iranian anti-imperialist forces,'' says the secretary-general of the pro-Soviet Tudeh, Nourredin Kianouri. The party supports the fundamentalists in the government, even though the Hodjatieh are strictly anticommunist.
Despite their very pro-Khomeini rhetoric, Iranian communists have to live semiclandestinely. Several of them have been arrested, some have even been executed. Still, the Tudeh is flexing its muscles. It is preparing for the next round.