King Hussein of Jordan made a one day visit to Syria today - the first leg of a mediation mission aimed at healing the split in Arab ranks caused by Egypt's direct dealing with Israel.

The king conferred in Damascus with Syrian President Hafez Assad before returning to Amman. He is due to fly to Cairo Thursday to confer with Egyptian President Anwar Sadat and later this week to Riyadh for talks with King Khaled of Saudi Arabia.

Although neither Hussein nor Assad said anything before or after their five-hour meeting today, observers were convinced the king's visit was an attempt to persuade Syria to attend the Cairo conference called by Sadat for next week.

Barring an unforeseen change of heart, however, Assad was not expected to participate in that meeting, which so far is limited to Egypt, Israel, the United States, and the United Nations.

Shortly after Hussein left Damascus, a Saudi Arabian statement said Assad will travel to Riyadh Thursday for talks with King Khaled.

Hussein's mission also reflected his distress at being torn between him nominal ally. Assad, and Sadat, whose visit to Jerusalem he has characterized as "courageous."

The king has avoided taking sides by refusing to take part in both the forthcoming Cairo meeting and the just completed Tripoli summit grouping Assad and other Arab leaders opposed to Sadat's policy.

Observers are convinced that Hussein is hoping for a reconciliation between Egypt and Syria that could allow him to once again play a major role in the Israeli-occupied West Bank, which Jordan ruled from 1948 to 1967.

In theory, Hussein abandoned any such hopes at the 1974 Arab League summit conference in Rabat, Morocco. Arab leaders then annointed the Palestine Liberation Organization as the sole legitimate representative of all Palestinians living in the West Bank and elsewhere.

Israel, however, is on record as opposing the creation of an independent Palestinian mini-state on the West Bank, although theoretically would not oppose the return of at least part of the territory to the King. This would dovetail with Hussein's old idea of a united Arab kingdom linking both the east and west banks of the Jordan in what once was Amman-ruled territory.

Sadat has not discouraged such thinking. During his visit to Jerusalem he failed to mention the PLO as such and he later heaped scorn on Palestinians in general.

The United States is believed to favor some kind of institutional links between Jordan and any West Bank entity freed of Israeli occupation.

Syria's attitude on this score is not known, but anxious Palestinians in past moments of crisis have accused Damascus of willingness to go along with the king's presumed desires.

Palestinians have never felt comfortable with Hussein since his army first tamed, then expelled the Palestinian guerrilla organizations during a series of bloody battles in 1970 and 1971.

Nor, despite the present tactical alliance between the PLO and Damascus have the Palestinians forgotten the Syrian army's actions against the guerrillas in the recent Lebanese civil war.

Cooperation between Jordan and Syria, former deadly enemies, began in 1975 in response to then Secretary of State Henry Kissinger's success in negotiating the so-called Sinai II disengagement deal. Even then, both Jordan and Syria felt Egypt had left them exposed as the major confrontation states open to the full brunt of Israeli armed forces.

Aside from a customs union and joint economic projects, Jordanian-Syrian cooperation has also included some military aspects.

Some degree of radar integration has been achieved to cover the north-western corner of Jordan, which is often described as likely path for an Israeli thrust toward Damascus.

Even on that score the effectiveness of such cooperation is open to question since Syria's Soviet built SAM ground to air missiles cannot be coordinated with the American Hawks Jordan is in the process of receiving.