Syria's Assad tries to dig himself out of diplomatic ditch. Damascus tries all-or-nothing strategy to counter setbacks at UN, Syria-Jordan tension

Syrian President Hafez Assad is playing ''all or nothing'' in pursuit of his two main foreign policy aims:

* To break out of the isolation in the Arab Middle East in which Syria has found itself, and to reassert Syria's longstanding self-proclaimed role as ''the throbbing heart of Arabdom.''

* To ensure that Syria has a central, and not a peripheral, role in any eventual new Middle East peacemaking effort, if (as Mr. Assad expects) the Camp David formula runs into deadlock on the Palestinian autonomy issue.

But Mr. Assad is playing his all-or-nothing game with a relatively weak hand. This has one possible and another certain consequence. First, he could end up with nothing. And second, to assert Syria's importance, he is limited in his options to mere spoiling operations.

In this context should be seen: the sudden upsurge in tension between Syria and Jordan, apparently provoked by Syria; Syria's counterproductive intransigence in the United Nations on Israel's virtual annexation of the Golan Heights; Syria's forcing of a postponement until next month of the Arab League foreign ministers' meeting planned for Tunis last weekend to consider the Golan question; Mr. Assad's role in wrecking the Arab summit in Fez, Morocco, last November, which was to have considered a Saudi peace plan; and even Syria's odd-man-out stance as the only Middle East Arab land backing Iran in its war with Iraq.

But Syria's weakness in conventional terms - due in large part to Syrian ''peacekeeping'' troops bogged down in Lebanon - still leaves Mr. Assad a remarkably astute and devious ''survivor.'' Although he belongs to Syria's Alawite minority, he has managed to keep himself in power longer than any other of his country's postwar rulers.

Mr. Assad's resentment of Jordan's King Hussein comes under three headings:

1. The Syrian President suspects Jordan of being a base for the Syrian fundamentalist Muslim Brotherhood, which has long been waging a campaign of assassination within Syria against Mr. Assad's Alawite minority.

2. Jordan stands by Iraq in the Gulf war and is a conduit for arms and other supplies to the Iraqi forces.

3. Mr. Assad finds it galling to see King Hussein relatively unencumbered by the Palestinian problem - even though Jordan ran the Palestinian West Bank till Israel seized it in 1967 - while Syria is so enmeshed in the problem that it must consider the Palestinians at nearly every turn.

Mr. Assad's latest round of efforts to establish a tough Arab role for Syria began with his introduction of Soviet-built SAM (surface-to-air) missiles into Lebanon last April. Israel reacted vigorously, threatening to destroy the missiles. The United States sent special envoy Philip C. Habib to the area to reduce tensions. He was successful, but Syria managed to keep its SAM missiles in Lebanon -- and they are still there.

That seemed a victory for Mr. Assad. But he was soon made to look ineffective. In July, Israel bombed the center of Beirut, killing many civilians. Despite the SAMs, Syria's reaction was confined to rhetoric.

In August, Crown Prince Fahd of Saudi Arabia announced his Middle East peace plan. Palestine Liberation Organization leader Yasser Arafat was reported to have been consulted in the drafting of it and to personally approve of it. Mr. Assad confided privately to a Western visitor at the time that he (Mr. Assad) could go along with the plan.

But when it came to public attitudes, Mr. Assad's perception of inter-Arab politics obliged him to speak differently. Even though the Saudis wooed him after publication of the plan, it remained a Saudi plan without Syrian input. So Mr. Assad boycotted the Fez summit in November, sending his foreign minister there to reject the Saudi proposals.

In December, Israel virtually annexed the Golan Heights. In the subsequent United Nations Security Council meeting to consider Syria's protest against the Israeli action, Mr. Assad had the fleeting satisfaction of seeing the US join in condemning Israel and calling for an Israeli withdrawal.

Israel ignored the call. Syria then sought mandatory sanctions against Israel. That proposal failed to get majority support in the Security Council. So Syria settled for a Council appeal for voluntary sanctions against Israel -- only to have that vetoed by the US.

In the meantime, Mr. Assad had sent his foreign minister to Moscow to seek Soviet help on the Golan question. But despite Syrian reports of new Soviet arms deliveries, everything points to a cautious Russian response limited to words. Once again, Mr. Assad has been made to look ineffective.

His efforts now are concentrated on getting the Golan question before an emergency session of the UN General Assembly. There nobody has the right of veto , and Syria can expect majority support against Israel. But the snag for Syria is that General Assembly resolutions are not binding.

Another snag is that Jordan is the only Arab member of the Security Council and has hitherto carried the ball there for Syria. Given the growing tension between the two, this must be irritating for Mr. Assad.

This piquant situation may help explain the failure so far to fix a date for a Security Council meeting to consider calling a General Assembly session on Golan. But whatever the explanation, the net result is another setback for the Syrian President - from which he presumably is trying to find a way to recoup or reassert himself.