Widespread shelling of Beirut's residential areas and the nearby mountains by rival Lebanese factions continued today, as Syria indicated a readiness to take at least provisional steps toward getting the combatants to accept a cease-fire.

At least 10 persons were reported killed in the capital today, and a barrage of shells hit Beirut International Airport, knocking it out of activity and setting ablaze a jetliner that passengers had been about to board.

Druze and Shiite Moslem Amal militiamen positioned in west Beirut, on strategic mountain ridges and in the Syrian-controlled western edge of the Bekaa Valley exchanged artillery and tank fire with Christian militias and Christian-controlled units of the Lebanese Army dug into strongholds northeast of Beirut.

The deaths brought the known casualty toll to 275 dead and 775 wounded since a series of car bombs hit Christian neighborhoods last week, setting off the fiercest round of sectarian hostilities since February 1984.

Syrian Vice President Abdul Halim Khaddam called Lebanese President Amin Gemayel and said a special security committee made up of representatives of Amal, the Druze Progressive Socialist Party, the Christian militias and the Lebanese Army would meet in the Syrian-controlled town of Shtawrah Thursday to work out a cease-fire.

The move by Syria, which all sides acknowledge as the country's current power-broker, came after three days of heavy fighting in which none of the chief combatants has shown a willingness to halt the hostilities.

Amal chief Nabih Berri had resisted all calls for a cease-fire after his west Beirut neighborhood came under intense shelling during the past two days. Berri said he had given orders for the shelling of Christian areas from positions in the Bekaa and the mountains yesterday, after concentrated barrages of mortars and rockets were lobbed into Moslem-dominated west Beirut.

Berri called for a military showdown and said he would not agree to a truce before "getting political and military guarantees that would prevent the repetition of what has happened."

Berri, who is the chief Shiite representative in Lebanon's national-unity Cabinet, reminded his Christian adversaries that "we are capable of decisive military action" and that "our artillery ramparts in the Bekaa and the mountains are ready and our forces prepared to advance."

Joseph Hashem, a Christian member of the Cabinet and a leader of the Phalangist Party, insisted today that "Syria has 80 percent of all political and military cards in Lebanon in its grip now."

Stressing that his side was convinced that most of the opportunities for a solution were in Syrian hands, while others saw Israel as the instigator of the current outbreak, Hashem asked: "How much longer do we have to wait? How many more lives and how much blood are needed to find out which of the two Syria or Israel shall win?"

Panic-stricken residents of Beirut's Shiite suburbs fled in long convoys to southern Lebanon today. Families sought refuge under highway bridges, garages and unexposed hallways, using brief lulls to make a run for the southbound motorways. Christian gunners fired barrages of long-range field artillery against the coastal stretch south of Beirut in retaliation for the pounding of Christian-controlled seaside towns north of the capital.

Whether Syria will succeed in silencing the guns firing out of regions it controls is a key concern of the Christian community, which says it is mystified by the uncontrolled onslaught from Syria's closest allies in Lebanon -- Amal and the Druze Progressive Socialist Party, headed by Walid Jumblatt.

Berri urgently summoned Jumblatt today to cut short a visit to the Soviet Union and return to Beirut.

Some analysts have interpreted the latest outburst of violence -- touched off by the two powerful car bombs in Christian regions last week -- as a kind of political pressure to squeeze the hesitant Christian camp into hastening the process of political change here.

They also have seen Syria's slowness to play the peacemaker as an indication by Damascus that it wanted the Christian militias further weakened first. Any meaningful political change in Lebanon would require the minority Christians to give up their dominant role in government.

The main power centers of the Christian camp, namely the executive committee of the Lebanese Forces, the main Christian militia, and former president Camille Chamoun, publicly have declared the need for a firm alliance with Syria, but such declarations do not enjoy wholehearted support in many Christian circles.

Some subscribe to a theory that Palestine Liberation Organization leader Yasser Arafat and his new Arab partners, or Israel, have much to gain if the Syrians trip again in Lebanon. This group argues that the influence of Syria is overestimated here.

But apart from the regional rivalries, the local bickering over constitutional changes still plays a significant role in the Lebanese leaders' calculations.

Berri is eager to push for radical changes in Lebanon's power structure to gain more rights for his Shiites, the country's largest sect.

Jumblatt, Berri's ally in opposition to Gemayel, has ruled out dialogue with any symbols of the Lebanese regime and seems content with territorial and military victories scored over the Christians during the past two years.

Jumblatt's militia is collecting road taxes, taking in money from Druze-run casinos and customs duties from ships docking at his new port in Khaldah, building tourist complexes and generally progressing in his emulation of the Christians' well-run ministate.

While other Moslem groups privately complain that Jumblatt's constituency -- only 7 percent of Lebanon's population of 3 million -- has made gains out of proportion to its size, Jumblatt is the strongest Lebanese leader on the scene. He enjoys virtually uncontested power in his tightly knit Druze community, support from the Soviet Union and financial backing from Libya and other regional forces.

Lebanon's Sunni Moslem community, with no paramilitary force comparable to the impressive militias of the Christians, Shiites or Druze, has been on the periphery of this new cycle of fighting, although its civilians have not been spared from the bloodshed that has victimized civilians evenly across Lebanon's patchwork of religious groups.

The suspension of flights from Beirut's airport after rockets shattered part of its terminal building and reduced a Middle East Airlines plane to a flaming ruin, was an ominous signal the Lebanese have known too well during the past 10 years.

The closing of the airport, Lebanon's only outlet to the world beyond its troubled region, has always been taken as an indication of fighting that went beyond the routine, and has always prompted a pessimistic new siege mentality among those left here to endure it.

Stephan Jaquemet, Swiss head of the International Red Cross office in Sidon, was freed after being kidnaped a day earlier by a brother of a Lebanese Shiite seized by the Israeli Army in March, Reuter said.