Jordan's King Hussein and Syrian President Hafez Assad met here today for the first time in six years for talks that could signal a significant reconciliation between two key Arab states that have been bitter enemies and could play a crucial role in determining if and how the Middle East peace process goes ahead.

In marked contrast to the tense state of Jordanian-Syrian relations that resulted in thousands of troops and tanks being deployed on both sides of the border in 1980, Assad welcomed Hussein warmly at the airport, then escorted him to the guest palace here. Scenes of the two men embracing were shown on television in both countries.

Later, the two met in closed session for several hours, while Jordanian Prime Minister Zeid Rifai and his Syrian counterpart, Abdul Rauf Qasim, conferred separately. Jordanian officials have said that the two countries are likely to exchange ambassadors soon. Jordan pulled its ambassador out of Syria three years ago.

No official details of the talks were immediately available, but diplomats, Palestine Liberation Organization officials and observers said the talks were certain to concentrate on three main issues: the Middle East peace process and Jordan's efforts to get it off the ground, the situation in Lebanon, and the thorny matter of who will represent the Palestinians in the peace process if discussions go ahead between a joint Jordanian-Palestinian delegation and Israel. Jordan has proposed that such talks be held, possibly within some kind of international forum.

The meeting here comes at a crucial time in the peace process, and it is not yet clear whether Hussein will use the occasion to try to soften Assad's strong opposition to including PLO Chairman Yasser Arafat in any talks or as a means to warn Arafat that Jordan will turn toward Syria unless the PLO chairman agrees to make the kind of concessions in the peace process that Hussein, Israel and the United States demand.

From the Syrian point of view, the talks here are undoubtedly seen as a way to move Jordan away from the accord reached last Feb. 11 between Arafat and Hussein to pursue a joint peace initiative with Israel.

Jordan and Syria have broken and restored ties four times in Hussein's 32-year rule. The most recent dispute began in 1979, when Assad accused Jordan of harboring Moslem fundamentalist opponents of the Syrian regime.

Today's talks represented the culmination of a slow process of rapproachement that began in mid-September under Saudi auspices when Rifai and Qasim held their first meeting in Jiddah, Saudi Arabia. They have met three times since. The Saudis have been seeking to resolve enough inter-Arab differences to set the stage for an Arab summit meeting for a broader discussion of regional peace efforts.

Aside from the issue of which Palestinians might be represented in any peace talks, Jordan and Syria remain divided over the five-year-old war between Iran and Iraq, with Hussein supporting Iraq and Assad supporting Iran.

Nevertheless, a western diplomat in Amman said shortly before Hussein's visit that "things seem to be going in the right track as far as atmospherics are concerned, and even on minor matters of substance."

Jordanian officials have insisted that their country's rapproachement with its Soviet-armed northern neighbor is aimed at drawing Syria into the peace efforts that Hussein is pursuing with the mainstream PLO on the one hand and Washington on the other.

Rather than an indication that Jordan is being influenced by Syria's opposition, the rapproachement is "an integral part of the peace process," aimed at softening Syria's stand, a senior Jordanian said recently.

The two sides agree that the Arab-Israeli conflict should be resolved at an international conference attended by all parties to the conflict and the five permanent U.N. Security Council members. But they disagree over who should represent the Palestinians.

Hussein wants Arafat's mainstream PLO to represent them. Syria, which opposes the mainstream PLO and Arafat, insists that a Syrian-backed four-member coalition including PLO dissidents opposed to Arafat's leadership should represent the Palestinians.

Jordan has so far rejected Syrian requests to abrogate its accord with Arafat, but appears to be using its rapprochement with Syria to pressure Arafat into endorsing U.N. Security Council Resolution 242, which calls for recognition of Israel's right to exist and its withdrawal from Arab lands it occupied in 1967. But 242 makes no direct reference to the Palestinians and their national rights, and Arafat has not publicly endorsed it, saying he first needs international guarantees that the Palestinians will be given self-determination within a confederation with Jordan as part of an overall settlement.

Leaders of three other Damascus-based PLO factions that have so far resisted Syrian pressure to join the rebels warn that Jordan, Egypt and the United States are trying to exclude the PLO from the peace process by demanding acceptance of 242.

Arafat's recognition of 242 would "cancel him personally and the PLO" from the peace process, said Nayef Hawatmeh, leader of the Marxist Democratic Front for the Liberation of Palestine.

Hawatmeh and others insist that Arafat "cancel all the deviationist steps" before reconciliation is possible. Their main objection is to the accord with Jordan, which they consider a sellout and a "mechanism to facilitate direct bilateral negotiations" between Israel and a Jordanian-Palestinian delegation instead of an international conference, Hawatmeh said in an interview.

Most mainstream PLO leaders say they hope Jordan will persuade Assad to accept them, but they are not optimistic. Others, such as Salah Khalaf, an aide to Arafat, have expressed fears that Syrian-Jordanian rapprochement could lead to an agreement to continue the peace process without the PLO.

The Syrian-backed PLO dissidents say that, on the basis of Syrian assurances, they feel that Syria's rapprochement with Jordan is only a "tactic" aimed at stalling Jordan from entering the U.S.-sponsored peace process, while gaining time and Jordanian backing for Syria's peace plan in Lebanon.