After lending its armed might to the Palestinians in southern Lebanon, Syria now wants the fighting stopped along Israel's northern border, informed sources said today.

Syria has reduced its artillery and rocket support for the Palestinians just as they are prepared to assault a key stronghold of rightist Christians, and has warned the Christian leaders to stop their close cooperation with Israel, according to Palestinian, Christian and diplomatic sources here.

"Syria accomplished its political aims. Now it wants everything to cool down there," said a western diplomat who has been working with what he called "the entire international community" to urge restraint on all sides - Syria, Israel, the Christians and the Palestinians - in southern Lebanon for fear the fighting there could develop into a full-scale Arab-Israeli war.

But there were no clear signs here tonight whether Syria would be able to work its will. There were reports from extremist Rejecion Front groups that Palestinian commandos already have begun a ground assault on the key Christian military fortress of Marjayoun, six miles from the Israeli border. Nor were there any indications of the Christian leaders' response to Syria's request that they restrict their now open and close collaboration with Israel.

But Palestinianin sources said today that "a political decision" has been made not to attack Marjayoun at this time. That word came as Palestine Liberation Organization chief Yasser Arafat and the PLO military commander in southern Lebanon, ABU Jihad, went to Damascus today to meet with Syrian President Hafez Assad.

Assad's personal envoy in Lebanon, Syrian Air Force intelligence chief Col. Mohammed Kholi conveyed Syria's displeasure with the Christian-Israeli alliance in separate meetings Friday with Lebanese President Elias Sarkis and Christian warlords, christian sources said.

Meanwhile, Palestinian artillery independent of Syria control continued its shelling of Marjayoun today and the Christians pounded Nabatiyah, a market town five miles to the west, and the villages of Ebles Saki and Khiam, from which the assault on Marjayoun would be launched.

Fiiday Palestinian commandos said that the objective of their-supported, Syria-supported week-long assault on Christian positions in the south was to break the security belt of Christian held towns protecting Israel from attacks over the Lebanese border.

With the recapture of the cross roads hill town of Taibe on Monday and Khiam on Thursday, the Palestinians achieved that objective.

According to a diplomatic source here, neither Syria nor the Palestinians recognized the strategic significance of Taibe - which controls a string of five other towns along the Israeli border and completes the security belt - until the Christians took it last week.

At that point Syria decided to support a Palestinian offensive in the south. Its heavy artillery and rockets were used to soften up Taibe.

This barrage came from known Syrian artillery positions and at first it was believed by diplomats, Palestinians and Christians that it has been fired by Syrians.

But now most experts here believe that the lanyard actually were pulled by members of Saiqa, the Syrian-controlled Palestinian group. About 75 per cent of Saiqa's fighters are also serving in the Syrian army, diplomats here said.

As a result, sources here said, Israel has had no excuse to retaliate against Syria. In fact, Syria did for the Palestinians exactly what Israel has been doing for the Christians in southern Lebanon - supplying logistical support, arms and some artillery support.

"It was a beautiful example of fighting by proxy," said a diplomatic source.

It also enabled Syria to settle a month-old grudge against Israel. In February, Israel used diplomatic saber-rattling to force the pullback of Syrian detachment of 600 troops and 10 tanks from Nabatiyah, which Israel said was too close to its border.

"That was a long, galling withdrawal for the Syrians, and now they showed the Israelis they are not dealing with a bunch of stumblebums," the diplomatic source said.

But the Israelis have made it clear through diplomatic channels that they will not tolerate Palestinian forces directly on their border.

The Israelis also want to keep open gates in the Lebanese-Israeli border fence that allow Lebanese to work and trade in Israel and Christian forces to get supplies there. These gates are still open, and it is unclear whether Syria's warning to the Christians means that they must be closed.

In any event, diplomatic analysts here believe, Syria has clearly gained in the southern campaign - especially in winning back its reputation among the Arabs as a supporter of the Palestinians after having fought the PLO in the Lebanon hills last fall and in the camps around Beirut in February.

The Syrians also showed the Christians that they have full control over the Palestinian fighters through their role as the mainstays of the Arab peace force that last November ended a 19-month civil war here.

Now, after a week of fighting ,the positions in the south are exactly as they were eight weeks ago, before the Christian drive.

The Syrians, according to diplomats here would like to see the offensive stopped. But the Palestinians, having tasted blood, want to take Marjayoun and get access to "Fatahland" - the rocky slopes of Mount Hermon from which they have mounted guerilla raids into Israel.