A second consecutive day of relative calm brought fragile hopes to Lebanon today that the month-long latest round of violence is about to be ended through negotiations.

Buoyed by the May Day holiday, politicians, newspaper editorials and citizens waxed enthusiastic about renewed Syrian-Lebanese negotiations due to start Sunday when Foreign Minister Abdel-Halim Khaddam of Syria returns from Damascus after a four-day absence from Beirut.

[Israeli warplanes flew across southern Lebanon, creating repeated sonic booms over the recently bombed cities of Sidon and Tyre, but stayed well away from the Bekaa Valley where Syria deployed SA6 and SA2 surface-to-air missiles earlier this week after Israeli jets shot down two Syrain helicopters, the Associated Press reported. A U.S. Embassy spokesman in Tel Aviv said Ambassador Samuel Lewis, meanwhile, spoke by telephone with Prime Minister Menachem Begin about American attempts to defuse the Israeli-Syrian confrontation over Lebanon.]

Ten artillery shells landed on Beirut airport, underlining Lebanon's continuing isolation. Flights have been stopped for 10 days because of shelling of the airport, which lies in Moslem-controlled western Beirut.

The shelling also underlined the limited nature of the optimism about a truce that would be built around a package deal whose integral parts in some cases had been accepted earlier only to fall into limbo when the crisis widened.

Detailed newspaper accounts of a working paper said to have the agreement of all warring Lebanese parties called for immediate security arrangements and long-term political steps.

Zahle, under Syrian siege since April 1, was to be occupied by politically neutral national security forces rather than Lebanese Army troops as the right-wing Christian militias had demanded. The militia inside the predominantly Greek Catholic city of 150,000 was to be banned, but it was unclear if the militiamen could remain without carrying weapons.

In return the Syrian peacekeeping troops were to leave the environs, although nothing was said about the positions they captured from the militia commanding the heights above the city on a hillside overlooking the fertile Bekaa Valley.

The Labanese Army was to take over the strategic Lebanon Mountains ridge line that Syrian troops stormed last weekend. Their presence there -- positioned to dominate the Bekaa Valley to the east and the Christian militia's heartland to the west -- prompted Israeli destruction of the two Syrian helicopters.

A Lebanese Army presence there is standard procedure during the summer months and would prevent militia or Syrian troops from claiming control.

The Lebanese Army also would take over responsibility for crossing points here in Beirut and extend its presence along the much-battered line dividing this capital in two sectors.

The chances for enlarged Army responsibility appeared enhanced by the dispatch of a further 200 troops yesterday to serve in southern Lebanon alongside United Nations peacekeepers there. An entire battalion of Lebanese troops is scheduled to be dispatched to the south before the end of May.

Some politicians and editorialists considered these measures could be carried out as early as Monday. But high militia officials privately said at least a week to 10 days will be needed.

They need that such practical measures are to a large extent tied to the much more delicate problem of winning some agreement between the Syrians and the Christian militias as well as bringing about political understandings in a country rent by warring groups, rival parties and leadership quarrels within various organizations.