Syrian suspicions run so deep that the state-controlled press routinely greeted Secretary of State Cyrus Vance today with accusations of carrying "an olive branch in one hand and stabbing people in the back with the other."

Unable or unwilling to believe that Egyptian President Anwar Sadat conceived his go-it-alone diplomacy by himself, the Syrian regime finds it easier to blame the United States.

Syria's penchant for believing in the conspiracy theory of history is rooted in the unusual nature of President Hafez Assad's government.

A member of the once despised Alawite sect of Islam and of the long-clandestine Baath Party. Assad has established a modern Syrian record for political tenure by staying in power for the past seven years.

Politically, Assad so far has handily outmaneuvered potential critics within the Baath Party, renegades in the service of his Iraq rivals, Communists, Nasserites and Moslem fanatics. This is no mean accomplishment for an Alawite whose community was once scorned by a Sunni Moslem majority that casts doubt on the Alawites' Islamic credentials.

Even before Sadat's latest "treason" - as the Jerusalem visit and its repercussions are called locally - relations between Cairo and Damascus had been through a series of ups and downs. Quite apart from a basic rivalry for primacy among Arabs relations had suffered from an ill-fated union in the late 1950s. In 1975, the Egyptian-Israeli withdrawal agreement known as Sinai III laid the groundwork for the suspicions and insults that surfaced again last month.

Even before Egypt all but officially opted out of the fight. Syria felt naked, faced with the full brunt of a beefed-up Israeli army.

Assad's involvement in Lebanon - where 30,000 Syrian troops are bogged down in what looks like an open-ended peace-keeping mission - has further weakened his military capabilities and fed suspicions that Syria is caught in a vast plot.

In Iraq to the east, Syria faces a government where historical rivalries are compounded by an obscure ideological battle between rival branches of the Baath Party.All this has reduced relations between the two to the worst of cold war tensions.

Syria's southern neighbor, Jordan, shows worrying signs of wanting to succumb to Sadat's blandishments. The Syrians are reported irritated with King Hussein, whom they helped rehabilitate in Arab councils after the isolation imposed when his army crushed the Palestinian guerrillas in 1970.

Although Assad proclaims the sanctity of the Palestinian cause, his own relations with the guerrillas have also been stormy.

In 1976 he did not hesitate to resort to arms to bring the Palestinians to heel when he felt they were getting out of control in Lebanon.

Even under the best of circumstances, Vance would have a difficult time in overcoming Assad's caution and suspicion. The Syrian leader's current situation, however has made Vance's job vastly more difficult.