Damascus, Syria — Literally overnight, Beirut seems to have reverted to rule by sectarian militia, sending all parties in the Lebanese crisis - internal, Arab, and Western - into a reassessment of their positions.
And as the murderous, 17-hour bout of artillery, rocket-propelled grenade,and rifle fire gave way to temporary calm Tuesday, much attention focused on neighboring Syria - seen as the key element in any negotiated moves to ensure renewed stability.
The Syrians' influence was seen as doubly important in light of signs that various other main outside players in the tangled Lebanese equation - notably Israel and the West Europeans - were seeking less direct involvement.
Israeli radio said Prime Minister Yitzhak Shamir had made clear to the US ambassador Tuesday that the Israelis would ''not intervene in Beirut'' despite the takeover of the western half of the city by Shiite and Druze militiamen and the accompanying defections from President Amin Gemayel's Army.
France and Italy, the American Marines' main partners in Lebanon's multinational peacekeeping force - or MNF - let known their intentions to take a fresh look at their commitments. Italy called for an urgent session of the participating nations in the MNF. The French were reported to favor the dispatch of United Nations troops to Lebanon - something that would require, among other things, the assent of the Soviets, since they hold a permanent Security Council seat.
The Reagan administration's plans were unclear at time of writing - although Western diplomats say the US has been sounding out Moscow in recent weeks on the UN option.
The US reaffirmed support for Mr. Gemayel. Yet with both the US Embassy mission and the Marines' Beirut positions ringed by Muslim militiamen, the Americans evacuated some 30 ''non-essential'' diplomatic personnel Tuesday to vessels off the capital's Mediterranean shore.
US envoy Donald Rumsfeld, having conferred with Gemayel, was expected to head for Damascus to meet with Syrian leaders. His arrival could not be confirmed.
In Lebanon, the country's Maronite Christian President Gemayel faced demands to resign from the triumphant Druze and Shiite militia leaders. His regular Army , painstakingly rebuilt with assistance from the US as an intended centerpiece for eventual Christian-Muslim entente, had virtually split into sectarian halves.
The sextent of Mr. Gemayel's control over non-government militiamen from his own Maronite Christian community remained unclear. Milia chief Fadi Frem was quoted as calling his men on ''alert'' - though there was no immediate sign of a relapse into the all out Christian Muslim milita battlers of 1975-76.
Whole units in predominantly Muslim west Beirut joined the militiamen. Some news reports said the Shiites and their Druze allies had also taken hold of the state radio and television facilities.
The main Shiite leader, Nabih Berri, called on his men to lay off foreign embassies, the MNF, and foreign residences, and generally to cease firing. But both he and Druze leader Walid Jumblatt were insistant, meanwhile, that Mr. Gemayel must step down and pave the way foir a restructured political setup.
At time of writing, Gemayel had given no indication whether he planned to step down. His foreign minister was reported heading for Saudi Arabia, presumably in hopes the Saudis might help mediate a truce with Gemayel's opponents. That route would almost surely lead through Damascus.
The Syrians, by late Tuesday, had given no clear indication of where they now stand on the question of Lebanon's political future - short of telling a delegation of mainstream Sunni Muslim politicans that Damascus would ''continue to support'' Lebanon. The assumption here is that if and when US envoy Rumsfeld arrives, the picture may become clearer.