Who are the terrorists behind planning, execution of Kuwaiti airliner hijacking?

It will probably be days or weeks before Western intelligence services can explain who is behind the hijacking of the Kuwaiti airliner. Western diplomats say the three groups most likely involved in the seven-day-old terrorist standoff in Tehran are: the Beirut-based Hezbullah (Party of God), the Islamic Jihad (Holy War), and the pro-Iranian Al Dawa group in Iraq.

All three movements recruit their members from Shiite Muslim Arab communities and claim they fight for the establishment in Arab countries of Islamic republics patterned on the Iranian model. The three are also known to have opted for violence to root out Western influence in the Middle East and have a record of bloody attacks. By Sunday, the hijackers claimed to have killed four hostages and threatened to kill four more. Some 146 of the orignial 160 passengers had been released to officials at Tehran's airport.

The Iranian government has repeatedly voiced its opposition to terrorism. In August this year, Ayatollah Khomeini solemnly condemned the hijacking of an Air France Boeing 737 to Tehran. ''How could we approve something that is against Islam?'' the Ayatollah asked. On Saturday the Iranian foreign affairs minister, Ali Akbar Velayati, repeated that his country disapproved of ''any hijacking by any group.''

However, the Iranian government never condemned the suicide attacks against United States and French military barracks in Beirut in October 1983. Those attacks were depicted in Tehran as ''acts of popular resistance.'' An Iranian editorialist even wrote that ''the American soldiers had died like Pharaohs under the rubble of their temple.''

Two months later, in December 1983, the Iranians announced in a communique they had nothing to do with attacks against the French and the US embassies in Kuwait. They refrained, however, from formally condemning the actions.

The United States government has repeatedly pointed to a connection between the groups and Mideast governments, particularly Iran. One European diplomat contacted in Tehran hints that the Iranians may, up to a point, have encouraged terrorist groups to hijack airliners belonging to conservative Arab countries.

This diplomat recalls that after a series of hijackings of Iranian airplanes by opponents of the Iranian government, the speaker of the Majlis (parliament), Hojatolislam Hashemi Rafsanjani, asked conservative Arab rulers to cooperate with the Iranian authorities to dishearten would-be hijackers. ''Otherwise,'' the speaker added, ''all air routes in the Persian Gulf area may become insecure.''

''A few days later,'' this Western diplomat continues, ''Iraqi security agents foiled an attempt to hijack one of their aircraft on a flight between Cyprus and Baghdad and, on Nov. 6, a Saudi Tristar was hijacked to Tehran.''

''The Iranians,'' this diplomat concludes, ''may have resorted to some kind of counterterrorism but we have to be very careful before accusing them. There may be coincidences, and groups they have helped in the past may have gone out of control.''

Addressing the faithful during last Friday's prayer meeting at Tehran University, a leading cleric, Ayatollah Mahdavi-Kani, asked: ''Why didn't the Arab sheikhs intervene when our aircraft were hijacked? If they want to avoid any new hijacking, they have to go to the heart of the matter.''

At time of writing Sunday, the Arab hijackers - believed to be three Lebanese and two Palestinans - still held 10 to 15 hostages on the Kuwait Airways Airbus. The hijackers were demanding the release of 17 men from Kuwaiti prisons, believed to be members of the pro-Iranian Al Dawa group in Iraq. Al Dawa was created several years ago by Shiite activists who wanted to topple Iraq's Saddam Hussein.

Since the outbreak of the Iran-Iraq war, Al Dawa has carried out several attempts against official buildings in Baghdad. Al Dawa is also believed to have links with the Tehran-based Council of the Iraqi Revolution whose spokesman is Hojatolislam Bagher Hakim.

A representative in Europe for the Lebanese Shiite movement Amal (Hope) explains: ''The Hezbullah group has no known leader and is rather unstructured. Its militants are former supporters of Amal who have been deceived by the moderate attitude of their leader Nabih Berri.

''Members of the Hezbullah,'' this representative continues, ''want an Islamic republic to be set up in Lebanon while Nabih Berri and most of Amal's members believe this is impossible in a multi-confessional country like ours.''

A Lebanese Shiite Muslim student contacted in Beirut says Hezbullah is very active in south Lebanon, where it has mounted many attacks against Israeli troops. ''In the past,'' this student explains, ''Hezbullah received money from Tehran, but the Syrians have apparently convinced the Iranians to reduce their support to groups challenging Berri's authority.'' This student also believes the group known as Islamic Jihad doesn't actually exist but is rather an umbrella title used by various terrorist organizations.

Last week, a man calling himself a representative of Islamic Jihad, telephoned the Beirut bureau of a Western press agency to say the hijackers should quickly leave Tehran so as not to tarnish the image of the Islamic Republic of Iran.

On Saturday, another man saying he was speaking for Islamic Jihad announced in Beirut that a hostage would be killed at Tehran airport every half hour unless the Kuwaiti authorities met the hijackers' demands for the release of the 17 jailed Islamic militants.

Early Sunday the hijackers demanded a new plane to take them out of Tehran.

They reportedly planted explosives in the wings and near the fuel tank, read their last will and testament, and said ''final prayers''.