The assassination of Palestinian leader Zohair Mohsen has lifted the curtain for a moment on the often shadowy terror war that has become an intimate and sometimes decisive part of Middle East politics.

Nowhere, it seems, is underground violence practiced with more regularity than in the land of the Bible, where most political leaders outside the hereditary kingdoms rose to prominence in independence or revolutionary movements for which plots, assassinations or sabotage were sometimes the only available tactics.

President Anwar Sadat of Egypt, for example, plotted violence against the British in the 1950s and Prime Minister Menachem Begin of Israel ordered terror bombings against them in Palestine in the 1940s. The leaders of Syria and Iraq for years dispatched against to bomb one another's capital in a blood feud between factions of the Baath Party.

Thus the attack on Mohsen was startling only for its setting - a luxury apartment in Cannes on the elegant French Riviera, far from the "Palestian struggle" in whose name Mohsen ran his Saiqa guerrilla organization.

There was little startling about the killing itself.Mohsen ranked high among Israeli intelligence's prime assassination targets for his role in the Palestine Liberation Organization of Yasser Arafat. His activities also had exposed him to the wrath of a number of powerful leaders within the Arab world and even his own Palestinian resistance movement.

Mohsen headed the PLO military department, which in principle directs the regular Palestine Liberation Army. He also sat on the 15-man PLO executive committee, which makes key PLO decisions and which Arafat heads as chairman. But it was his leadership of the Saiqa guerrilla group that gave him his prominence and power.

Saiqa, "lightning" in Arabic, is less numerous and powerful than Fatah, the main PLO guerrilla group led directly by Arafat. It is the Syrian wing of the guerrilla movement, trained, led and at times given orders by Syrians.

Israeli leaders thus had two reasons for wanting Mohsen dead, his prominence as a Palestinian chieftain and his group's role as an unofficial armed force for the Syrian government of President Hafez Assad.

Israeli agents had already hit high in the organization. Three of its top leaders - Youssef Najjar, Kamal Nasser and Kalam Adwan - were slain by an Israeli squad that landed by boat at Beirut in May 1973.

Only last January, an explosion in Beirut widely attributed to an Israeli team killed Ali Hassan Salamah, or Abu Hassan, the flamboyant chief of Fatah security was was reported to have organized the terrorist operation against Israeli athletes at the 1972 Munich Olympics.

Several lower-ranking Palestinians have been killed in European capitals in assassinations attributed to Israelis. But a number of similar murders - including those of the PLO representatives in London and Paris - are believed to have been the result of bitter rivalry between factions of the Palestinian movement.

Ibrahim Qalaq, the PLO delegate murdered last year in Paris, for example, was slain by a fellow Palestinian reported by French police to be working for a pro-Iraqi group struggling against the relatively moderate-line adopted by Arafat and propounded among the French with quiet insistence by Qalaq.

The Iraqi-backed Palestinians were for a number of years led by Dr. Wadie Haddad, a physician trained at the American University of Beirut who broke with Habash in a dispute about advocacy of extremist terror opreations. After Haddad recently was reported to have died of disease in East Germany, the Baghdad-based operations were said to be controlled by Abu Nidal, a mild-speaking, former PLO official whom the Arafat group condemned to death for extremist tactics within the organization.

As a close follower of Syrian President Assad, Mohsen could have become a target of these groups during the years of rivalry between Baghdad and Damascus. The two neighbors recently have abandoned their feud, however, and the retributions between their respective Palestinian followers are said to have ceased.

A more immediate Arab reason to want Mohsen dead existed here in Egypt, where there was a strong public outcry against Saiga after the occupation of the Egyptian embassy in Ankara on June 13.

The Ankara occupation was carried out by Palestinians identifying themselves as "Eagles of the Palestinian Revolution." The group, a little-known terror squad, is said to be a branch of Mohsen's Saiqa and, by extension, of the Syrian armed forces.

Prime Minister Mustafa Khalil quickly vowed retaliation against the PLO, and the popular Egyptian press shouted in big headlines for revenge. Then, apparently on orders from Sadat, Khalil softened his remarkes about the PLO and the press veered its outrage toward Syria.

Observers speculated than that, with military action apparently out of the question and little other leverage, Egypt could resort to underground tactics to carry out Sadat's repeated warning to his Arab foes: "For each blow, we will strike one thousand blows."