Brussels — A triumvirate rule has emerged in Iran, with Ayatollah Ruhollah Khomeini sitting on the political sidelines, say Western observers contacted in Tehran. The three leaders - speaker of the parliament Hashemi Rafsanjani, Prime Minister Hossein Mussavi, and President Ali Khamenei - have apparently put aside their disputes over the war with Iraq and agreed on a strategy:
1. Iran first favors a political solution to the nearly four-year-old conflict.
2. But such a solution requires the removal from office of Iraqi President Saddam Hussein.
3. If Mr. Hussein's departure cannot be obtained through diplomatic channels, Iran should launch a large ground offensive into Iraq.
Ayatollah Khomeini remains, of course, the religious leader of the country, but he is less and less involved in day-to-day decisionmaking. This is evident in the Iranian press, whose coverage of the Ayatollah's activities over the past few months has dwindled.
The Ayatollah receives fewer citizens and officials in his home outside Tehran. He now speaks in public only once a month, and when he does speak, he talks only about vague religious subjects. The only issue on which he stands firm is the Persian Gulf war: There is to be no compromise with Saddam Hussein, he insists.
Also, open discussion on who will succeed the Ayatollah is no longer taboo. Mr. Rafsanjani recently said in public that he believes ''Ayatollah (Hossein Ali) Montazeri has the required qualities to become Iran's next religious guide.'' Ayatollah Montazeri has long been considered Khomeini's heir-apparent.
Last month's shakeup in the parliament (Majlis) was seen as a boost for Prime Minister Mussavi's political prospects. He was known to be eager to get rid of some of his most conservative Cabinet ministers. In a parliamentary vote of no confidence, five ministers lost their jobs, among them Defense Minister Muhammad Salimi and Education Minister Ali Akbar Parvaresh.
The sacked ministers are all said to have close ties with a group called Hodjatieh. Its members are known for their support of a strictly Islamic society , opposition to state involvement in the economy, and persecution of the Bahai religious minority. The group, which was formed during the imperial regime of the Shah, opposes participation by the clergy in secular matters.
A few days after the Cabinet shakeup, Mussavi appointed some of his closest political allies to fill the vacant posts. Western observers in the Iranian capital were surprised, having believed that Mussavi's influence was on the decline.
Rafsanjani also enjoys strong political support, having won a parliamentary vote of confidence with an overwhelming majority. Still, in ousting the five Cabinet ministers, the deputies apparently wanted to assert their political independence from Rafsanjani. Moments before the vote, Rafsanjani urged his colleagues to vote for all members of the Cabinet.
''A Cabinet shakeup,'' Rafsanjani said, would ''weaken the country at a crucial stage of the war with Iraq.''
For the first time since the 1979 revolution, the Cabinet now includes a minister of information, Hojatolislam Mohammadi Reyshahri, who was a prosecutor in Iran's military revolutionary courts. He will be in charge of a new intelligence service.
''Gathering of information about our enemies inside and outside Iran has been one of our weak spots,'' explains an Iranian official contacted in Tehran. ''Until now we have had various and often inefficient intelligence agencies subordinated to different revolutionary organizations.''
Exiled opponents of the Iranian regime say Mr. Reyshahri, who is known to be an Islamic hard-liner, will pattern his new Information Ministry after the Savak , the defunct imperial secret police.
Travelers coming from Tehran report that a new campaign has been launched to enforce a strict Islamic dress code. Groups of extremists wandered through Tehran's well-off neighborhoods last month and clubbed women whose hair was not entirely covered by scarves. The government condemned the violence, but, to show it still supports Islamicization, it organized nonviolent demonstrations a few days later throughout the country to protest ''immodestly dressed women.''
''The regime is encouraging women to wear chadors instead of scarves,'' says an Iranian woman contacted in Tehran. The chador is a large black sheet worn by women that completely covers the body.
''Working in a factory or in an office while wearing a chador,'' the woman says, ''would be almost impossible because you have to keep it tightly closed with one of your hands. The compulsory wearing of the chador would thus have important social and economic consequences.''
Meanwhile, Iranian officials have had to contend with a spate of hijackings and defections in the past several months. Since July 1983 eight aircrafts belonging either to the Iranian Army or to the state airline, Iran Air, have been hijacked or commandeered to another country. The latest incident occurred last week, when two Iranian pilots flew their jet fighters to Iraq and defected.
European diplomats in Tehran say that no organized opposition movement is behind the hijackings. Most of the hijackers are Iranian Army officers who oppose the continuation of the war.