Amid reports that Syria has begun a tentative withdrawal of troops from its side of the border here, Jordanian forces today continued to dig into defensive positions.

Jordanian sources said they do not believe the Syrian Army has actually begun a pullback, despite reports from travelers that Syrian tank carriers and heavy gun trailers were seen moving away from the frontier and statements by Syrian officials that a quarter of the Syrian and Jordanian forces have withdrawn.

The Syrian officials' comments were taken in Damascus to mean the two-week border crisis was at an end, according to wire service reports. But observers here stressed that the Syrian troop movements could merely be redeployment of isolated units in the border area.

There was no eveidence here that the Jordanians have moved any of their tanks, artillery and armored vehicles, and the government continued to maintain that there would be no pullback until the last Syrian unit has withdrawn.

Tanks and artillery emplacements were sparsely dispersed along an approximately 25-mile-long line well within the frontier, between the towns of Irbid and Mafraq. Although the Jordanians are said to have 30,000 troops along the border, what is there is so thinly spread that it is difficult to ascertain the numbers. Army officers refuse to talk with reporters visiting the frontier.

In many places, solitary tanks, the barrels of their guns poking over crude earthworks, are placed a mile or more from each other.

As a result of a similar deployment of the Syrian forces deep within that side of the frontier, there is no atmosphere of face-to-face confrontation to match the rhetoric coming out of Damascus and Amman.

Observers said it is highly unlikely that Jordanian King Hussein will back-track from his refusal to withdraw unilaterally, because he feels the confrontation was precipitated by Syrian President Hafez Assad and that it is Assad's responsibility to act first.

Syria began moving two divisions to the border Nov. 20, just before the 11th Arab summit meeting convened in Amman, and Assad says he acted because Jordan was giving assistance to the fundamentalist Moslem Brotherhood, which has been responsible for a wave of bombings and assassinations in Syria.

However, Jordan denies that it has supported Syrian Moslem Brotherhood members, and officials here, including Hussein, have suggested obliquely that the Soviet Union may be behind the Syrian moves.

Much of the suspicion about the Soviets appears to stem from the friendship treaty Syria and the Soviet Union signed earlier this year and longstanding fears on the part of conservative Arab monarchies of an increased Soviet presence in the Middle East.

These fears were expected to be part of the discussions at an Islamic summit that a key adviser to Yasser Arafat of the Palestine Liberation Organization said will convene in Saudi Arabia on Jan. 24. The adviser, Khalid Hassan, told a Beirut magazine that Arab leaders who attend the Mecca gathering might use the occasion to try patching up the differences that were so evident at their recent summit.

However, sources in Jordan said it is impossible to project when the confrontation between the Syrian and Jordanian armies will be eased wtihout knowing for certain Assad's real motive for moving his troops forward.

If the motive were merely to scuttle the Arab summit, which Syria boycotted because of worsening relations between the two countries since the beginning of the Iraqi-Iranian war, then there would appear to be little reason for Assad to keep his Army on the border.

"It's costly to keep an army out of garrison, and there is a potential morale problem with the troops. The one thing Assad doesn't need is unrest in his Army," said a knowledgeable source here.

However, if the motive were to divert Hussein's attention from the Palestinian issue and keep him from entering into a new peace initiative that would include Jordan, then the troop deployment could be expected to last indefinitely, some observers suggested.

Also, a protracted confrontation would be likely if the Syrian Army move were made in league with Iran, which Syria is tacitly supporting in the gulf conflict, sources said. The same could be expected if Assad's goal were to divert attention from his own internal political problems and diffuse opposition to his government from within Syria.