The first meeting between Jordan's King Hussein and Syrian President Hafez Assad in almost six years is expected to take place in Damascus "before Christmas," Jordanian Foreign Minister Taher Masri said today.

But according to senior Jordanian officials, most key issues remain to be resolved between the prowestern monarch here and the Soviet-armed Syrian president.

"We have improved the atmosphere, we have improved the bilateral relations, but the differences are still there," said one senior Jordanian official.

Jordan's hope, he said, is that the encounter will be viewed as "another big and important step in the efforts of Jordan to facilitate and to push the peace process."

But Syria has shown little inclination to budge toward a more conciliatory stand in the process or to forgo its strong opposition to Palestine Liberation Organization Chairman Yasser Arafat, the king's current partner in attempts to normalize relations with Israel.

After two preliminary meetings between the Jordanian and Syrian prime ministers in Saudi Arabia and an extended session between Jordanian Prime Minister Zaid Rifai and Assad in Damascus two weeks ago, Jordan has concluded that only a summit is likely to begin resolving the basic impasse, this official suggested.

The Jordanian move, as the Jordanians describe it privately, has two basic objectives.

One is to put pressure on Arafat, whom the king has come to view as increasingly intransigent in the peace process because of Arafat's continued unwillingness to accept publicly U.N. Security Council Resolutions 242 and 338, effectively guaranteeing Israel's right to exist.

The other is to try to persuade Syria to join in the peace process as a participant in an international conference that the Jordanians believe is essential as a next step.

The king has sought an international forum, including the Soviet Union, as the setting for negotiations with Israel and the guarantor of the results. In a limited context, Israeli Prime Minister Shimon Peres has accepted the principle of an international forum but only to facilitate direct Israeli-Jordanian talks.

Syria, as the Soviets' main client in the region, would presumably play a central role if Moscow were to attend.

Masri went so far today as to say that Washington also believes Syrian participation is essential in the long run, although most of the thrust of American policy has been to keep the Syrians at arms length while pushing alongside Israel for direct bilateral Israeli-Jordanian negotiations.

"The Syrians are a major part of the conflict , and we have agreed with the Americans that they should participate in the peace process ," Masri said.

Richard W. Murphy, assistant secretary of state for Near Eastern affairs today is completing a visit here as part of a tour briefing the region's officials on the outcome of the Geneva summit between President Reagan and Soviet leader Mikhail Gorbachev.

Some western diplomats here suggest that the participation of Syria in an international conference might make it possible for Hussein to exclude Arafat, whom the Israelis refuse to deal with, in favor of other Palestinian or PLO representatives. But it is unclear how the king might do this in the current Arab political environment.

Another imponderable is how a conference might be arranged that would include both Arafat and Assad. "We know that the position of Assad himself toward Arafat is irreconcilable," said one senior Jordanian official.

In an effort to improve its hopes of winning concessions from Assad, Jordan in the past month has made what some Arab diplomats consider extraordinary gestures aimed at mollifying the Syrian president, while getting little from Syria in return.

The most dramatic move came on Nov. 10, just before Rifai's trip to Damascus, when King Hussein acknowledged that Moslem fundamentalist terrorists responsible for a number of killings in Syria during the past decade, had found refuge in Jordan.

Although Jordan's security forces usually keep a close watch on potential terrorists, the king insisted in a message to his prime minister was made public here that he had not known that these anti-Syrian groups were in his country.

Assad repeatedly had accused Jordan of training as well as harboring members of the Moslem Brotherhood, and in 1980 resulting tensions led to a major military build-up on both sides of the border.

But Syria also was believed by many Jordanian officials to be behind some attempts against Jordanian diplomats and attacks on its national airline. According to officials here, Assad has denied involvement in these and offered no firm guarantees that there will be no attacks in the future.

Today, the Jordanian Interior Ministry announced that Jordanians traveling to Syria will no longer need special permits, thus ending a policy in effect since late 1983 when it was feared that Syria might take drastic actions to halt the then warming relationship between Jordan and the PLO.

Before the Hussein-Assad meeting, another set of talks is expected here between Prime Minister Rifai and Syrian Prime Minister Abdul Rauf Qasim. Officials said the exact date of that meeting has not yet been fixed.