About 18,000 Christians have fled recent fighting in their home towns around Sidon and settled temporarily in the towns and villages in the part of southern Lebanon still under Israeli control.

The hastily erected camps of tents, the overcrowded schools and churches, the blank stares and mumbled curses of the refugees gathered here and in nearby communities testify to the latest turn of events in the continuing violence that has been sweeping over Lebanon in waves for the past decade.

According to Israeli Army estimates, there are 4,000 Christian refugees here in Marjayoun, 3,000 in nearby Kelea and a total of 18,000 scattered among the Christian communities that dot the landscape of the security zone along the Israeli-Lebanese border. More than half of them are children under the age of 15.

The Christians, members of what has been Lebanon's most prosperous community, left after Samir Geagea, a commander of the Christian Phalangist militia, pulled his men out of the area, and their villages were attacked by Druze, Moslem and Palestinian militiamen. They now wait here without much hope of returning soon to their homes. Many of them blame Lebanon's Christian president, Amin Gemayel, for allowing them to be driven from their homes.

Laundry, the white shirts and blouses of children, was hanging like flags of surrender outside the windows of classrooms at the Sacred Heart School here today. Inside one of the rooms, an old man sat awkwardly on a small chair meant for a child, his face impassive as he concentrated on smoking the cigarette in his hand.

There were no classes today at the Sacred Heart School, nor were any games played on the soccer field in the nearby village of Kelea. The soccer field was filled with 15 large Israeli Army tents, between which were strung ropes that held more laundry to dry in the midmorning sun.

Inside one of the tents, a man dressed in striped pajamas sat on a thin mattress on the ground and cursed President Gemayel.

"He is responsible for ruining this country," the man said. "He is a dog."

The clash of the militias and the flight of refugees have become part of the Lebanese national fabric, related in matter-of-fact tones today by Rashid Simon, 57.

He is from the village of Miyumiye, adjacent to a Palestinian refugee camp near Sidon. When the Phalangist militiamen pulled out, the Palestinians attacked, burning the Christian village. They attacked because three years ago, when the Israelis were in charge and the Christians were riding high, the villagers burned part of the refugee camp. The Christians did that because 10 years earlier, Palestinians had killed five persons in the village.

Simon did not seem to regret the 1982 attack on the refugee camp or to be surprised that the Palestinians retaliated when their time came last week.

In the current turmoil, more than 20,000 refugees made their way to Jezzin, a major Christian center north of here that is outside the Israeli security zone and is still threatened by Druze and Moslem militias about seven miles to the west. Others chose not to gamble on whether Jezzin would hold and fled as far as they could, to nestle in relative security within a few miles of the Israeli border.

By today, although there was fighting in Beirut, there appeared to be a lull in warfare in southern Lebanon, and local residents and Israeli Army officers here reported that the flow of refugees from the north had slowed to a trickle. Some Jezzin residents who came south as the fighting neared the town reportedly were returning to their homes, while other refugees in Jezzin were said to be attempting to make their way to Beirut.

But the lull may not last, and the Christian refugees are now looking for help to one man -- Brig. Gen. Antoine Lahad, commander of the South Lebanon Army -- and beyond him to Lahad's sponsors and supporters, the Israelis.

Lahad, who is in Jezzin with some of his units, has vowed to defend the town. But Lebanese Moslem leaders have made a withdrawal from Jezzin by the South Lebanon Army part of their price for agreeing to halt the fighting.

The Christians here, who said they felt betrayed by Geagea and Gemayel, both Christians, and by the earlier promises of tranquility from Druze and Moslem leaders, want no part of such a deal.

"It will be safe if Lahad stays there," said Fayez Abboud, 53, a resident of Jezzin who came here in search of relatives. "But when Lahad leaves, we will leave."

As for promises from the Moslems, Abboud said, "For 11 years, every agreement with the Moslems, the Christians lose."

The Israelis have given the Christians no reason to think they will intervene in the fighting, but they are clearly allowing Lahad a free hand in Jezzin.

"Lahad can do whatever he wants, and so far he is doing a good job," said an Israeli officer.

The rapid and unexpected influx of refugees here has transformed this normally placid community into a center of bustling activity. The streets were clogged today with the overloaded, dusty automobiles of the refugees, Israeli Army trucks and jeeps, and vehicles that belong to the International Committee of the Red Cross.

Some of the refugees are sleeping in their cars, but most have found shelter in school classrooms, churches and private homes. In the past several days, tons of flour, rice, sugar, meat and cooking oil have been brought in, at first by the Israeli Army and more recently by a Red Cross convoy from Beirut.

But they do not know how long they will be here, or where else they can go. Israel is aiding them, but the Israeli assistance stops at the border, which is closed to the refugees.

"I don't think the Israeli government would want them, and they would not feel welcome in Israel," said Elias Hourani, a shopkeeper from Ain Kharoub who described himself as a spokesman for the refugees. "They want to be among their own people, in Beirut."

Standing in the main hall of the school, Hourani said the latest setbacks suffered by the Christians were the fault of their leaders and "the mistakes of governments."

"Why do these people have to suffer from the mistakes of governments?" he asked. "It will take time to explain that they will not be going back in the near future."