Sporadic sniper fire crackled in the Shiite Moslem slums Tuesday and rival militiamen fortified their positions, apparently convinced that a truce arranged by the Syrian army would not last. Families streamed out of the ramshackle 16 square miles of south Beirut, carrying mattresses, bundles of clothing and other possessions. About 250,000 Shiites lived in the slums before the battle began last Friday, but police said 60 percent had fled by Tuesday. The 18 foreign hostages in Lebanon, including nine Americans, are also thought to be held captive in the slums. Police reported five people wounded by sniper fire. Gone at least temporarily were the tank, mortar and rocket duels between the Shiite militias Amal and Hezbollah that killed at least 154 people and wounded 372 in the previous four days. Before dawn, 36 Syrian officers moved into the area with six committees to man truce observation posts. Police said each committee included an Iranian Embassy official, a representative of Amal and another of Hezbollah. Amal, a mainstream militia backed by Syria, and the radical, pro-Iranian Hezbollah are fighting for control of the slums. Amal is Arabic for Hope and Hezbollah means Party of God. Syria and Iran, allies in public, are competing behind the scenes for influence with the 1.2 million Shiites, Lebanon's largest sect. President Hafez Assad of Syria keeps 25,000 soldiers in Lebanon, including 7,500 in Beirut. After 13 years of civil war, he was the country's undisputed power broker until Iran began challenging the Syrian position. There still was no word Tuesday on the fate of the hostages, most of whom are believed held by kidnappers linked to Hezbollah. A police source said it was ``physically impossible'' for hostages to have been smuggled out because Amal and the Syrian army control the slum exits. The Syrians sent 7,500 soldiers to Moslem west Beirut in February 1987 to stop a factional war in which the two main elements were Amal and the Druse militia led by Walid Jumblatt. They drove Hezbollah militiamen from some outposts in west Beirut but have stayed out of the southern Shiite slums. Syria's military intelligence chief in Lebanon said Tuesday, however: ``It is impermissible to let the current state of affairs continue.'' When asked whether soldiers would be sent into the slums if the fighting did not stop, Brig. Gen. Ghazi Kenaan said: ``We hope it won't come to that, but we shall not allow the bloodshed to continue.'' A Lebanese police spokesman, whose name cannot be revealed because of regulations, said the truce committees were ``trying to convince the warring factions to observe a cease-fire as a first step.'' The three-point truce plan announced Monday calls for a cease-fire, pulling militiamen off the streets and a return to positions held before the battle began. Hezbollah, which has gained control of about half the slum area since Friday, ``rejects the return to pre-Friday positions,'' the police spokesman said Tuesday. Militiamen of Hezbollah were seen fortifying their positions with earthworks in the densely populated districts Ghobeiri, Bir el-Abed and Hay Madi. Amal controls the Haret Hreik, Mreiji, Roweiss, Shiyah and Kasskass districts, plus the main gateways into the slums. According to the police spokesman, Amal moved in 1,000 more fighters from the Bekaa Valley in east Lebanon, a main base for the Syrian army. The ancient city of Baalbek in the Bekaa is a Hezbollah stronghold. ``It appears that both sides are preparing for another round of fighting,'' the police spokesman said. How many combatants have been involved on both sides is unclear. A police source said Hezbollah could put about 5,000 men in the field, but Amal is believed to be larger and has a broader following among the Shiites. Ibrahim Sarhan, a vegetable vendor, and his wife and four children walked out of the slums Tuesday carrying mattresses and clothes. ``We have been living in a basement since Friday,'' he said. ``I think this is the beginning of a long battle. We will come back when this is over.'' Mohammed Milhem, a 30-year-old grocer, was trying to patch a bullet hole in his car's gas tank. ``We need the car to get out of here,'' he said. His wife and three daughters were packing the car with mattresses, clothing, a television set and a sewing machine. Some of those who flee have family or friends elsewhere in Lebanon. Others camp out on the streets of west Beirut or take refuge in schools, mosques or sports stadiums.