For the first time in many weeks, Mideast diplomacy has at least briefly seized center stage from Mideast gunfire. Yet despite some New Year's signs of hope on two fronts - Lebanon and the festering problem of the Palestinians - potentially serious obstacles to a negotiated settlement remain.
Particularly complex is the relationship between the Reagan administration and Syrian President Hafez Assad - despite Mr. Assad's release last Tuesday of a captive US pilot and Washington's subsequent muting of recent public criticism of the Syrians.
In addition to the release of Lt. Robert Goodman, a move clearly aimed largely at encouraging pressure for an early withdrawal of US peacekeeping troops from Lebanon, other political or diplomatic developments have encouraged some cautious hope in the Mideast. They include:
* Reports from Lebanon of progress in negotiating a ''security plan'' that would disengage rival Christian and Muslim militias and might help extend the authority of Lebanon's hard-pressed central government.
* King Hussein's decision to reconvene Jordan's parliament, including Palestinian deputies from the Israeli-occupied West Bank, for the first time since 1974. The move is seen by diplomats as a possible sign that the King, who is expected to resume talks with Palestine Liberation Organization leader Yasser Arafat soon, may be ready to play a role in US-mediated peace efforts.
* Mr. Arafat's apparently successful weathering, within his Fatah guerrilla group, of criticism for his recent reconciliation meeting with Egyptian President Hosni Mubarak.
At time of writing, fighting among various of Lebanon's many rival forces afforded a reminder of how great are the obstacles to peace.
Gunfire, presumably from antigov-ernment Muslim militants, killed a US marine Sunday near the Lebanese capital's Mediterranean shore. The regular Lebanese army came under fire over the weekend from Druze and Shiite Muslim opponents outside Beirut. And in the north Lebanese port city of Tripoli, Syrian-supported local militiamen intermittently have been battling Muslim guerrillas who sided with Arafat in last month's intra-Palestinian fighting there.
Still, the foreign ministers of Lebanon, Saudi Arabia, and Syria met Sunday in Riyadh to discuss the proposed new ''security plan'' and possible moves to reconvene a Lebanon reconciliation conference that first met briefly in November.
Nabih Berri, who heads the largest force of Lebanese Shiites, was quoted as saying he and other Muslim leaders had accepted a ''final version'' of the security plan during talks in Syria.
The Syrians remain the key to both the security plan and serious moves toward political reconciliation in Lebanon.
Syria maintains some 40,000 troops in neighboring Lebanon, introduced in 1976 at the end of an 18-month civil war there. Syria also provides backing for Mr. Gemayel's Muslim opponents, fearful of what Damascus terms a joint US-Israeli effort to dictate to Gemayel a settlement perpetuating Israel's military presence in Lebanon and excluding the Syrians.
The Syrians assume that, if only because of domestic US political pressure, Mr. Reagan will move to withdraw his Marine contingent from Lebanon. The Israelis, too, are under domestic pressure to withdraw at least partly from the large area of southern Lebanon occupied since Israel's invasion in June 1982. Israeli forces have taken more casualties recently, and the Lebanon occupation is further straining Israel's troubled economy.
But the message of resurgent violence in Lebanon in recent weeks - following the souring of a brief move toward entente by Gemayel and Damascus - is that only a long-term arrangement acceptable to the Syrians has much chance of success.
Since the release of the US pilot, on intercession by Democratic Party presidential candidate Jesse Jackson, the Reagan administration has taken a generally conciliatory tone toward the Syrians.
But the US has also pledged to continue reconnaissance flights over Syrian-controlled areas of Lebanon - a catalyst for recent US-Syrian exchanges of fire. And it remains unclear whether the softened public tone presages any workable US-Syrian entente. One early sign may come during an expected visit to Syria by US Mideast envoy Donald Rumsfeld.
The Syrians also hold a potential veto on wider efforts to revive negotiations on the Palestinian question. Syria is seen as likely to oppose - perhaps with guns and bullets in Lebanon - the very kind of negotiating initiative the US wants King Hussein to support.
A renewed US-mediated effort to resolve the issue of the formerly Jordanian West Bank, especially if based on a September 1982 Reagan peace plan attacked by Syria, would reinforce fears in Damascus of an overall settlement leaving Syria out in the cold. The Syrians want an end to Israeli occupation of their Golan Heights, captured by Israel along with the West Bank and Gaza Strip in the 1967 Mideast war, as part of any settlement.
Jordan's King Hussein, encouraged partly by last month's Arafat-Mubarak meeting, has signaled his readiness to reopen talks with the PLO leader on a joint Mideast strategy. The reconvening of the Jordanian parliament, which fell fallow after a joint 1974 decision by Arab countries to give the PLO a sole mandate to represent the Palestinians, seems an implicit notice to Arafat that the King may go it alone at the negotiating table if the PLO balks much longer at attempting a negotiated settlement.
But the King, looking over his shoulder at Syria and aware that the Israelis have publicly ruled out any major West Bank concessions in future talks, may hesitate to follow through on this signal to Arafat.
And Arafat remains so far publicly opposed to the US peace plan. A recent meeting of his Fatah group ended with no clear signal of future policy toward King Hussein, although it did stop short of challenging Arafat's leadership over his controversial visit to Egypt.