The cease-fire that halted the fighting in southern Lebanon last month is in danger of disintegrating despite intensive negotiations this week to resolve disputes over what the truce meant and how to implement it.

Although the parties to the agreement keep pledging to abide by it, sporadic shelling and shooting incidents have been reported throughout the week.

Except for the withdrawal from Lebanon of Israeli troops and tanks that crossed the border last month to fight on the side of Lebanese Christian militiamen against their Palestinian and Lebanese Moslem opponents, the situation has not changed since the cease-fire went into effect Sept. 26.

According to Palestinian and Lebanese officials and informed diplomatic sources, disagreements over the number of Palestinian guerrillas allowed to remain in the south, the role of the Christians in the new national army and the conditions under which that army will move into the area have all combined to thwart the implementation of the agreement.

In addition, these sources say, there is a dispute over the so-called "good fence." Israel's policy of allowing Lebanese to come across the border to work, shop and receive medical care. The Israelis and many of their Christian allies want to keep the border open after the Lebanese army moves in to take control of the border area, as the cease-fire calls for, but the Lebanese Moslems, the Palestinians and Syria are asking that it be closed.

At issue is the final phase of the "Shtaura agreement," signed in July by Syria, Lebanon and the Palestinians. Under the accord, the Palestinians are required to withdraw most of their forces from the border area and units of the Lebanese army are to go south to establish the authority of the central government in the area.

Lebanese President Elias Sarkis and his prime minister, Selim Hoss, have been hinting all week that the army's move is imminent, but there is no evidence to support that.

The Palestinian News Agency, WAFA, [WORD ILLEGIBLE] today that the leadership of the Palestine Liberation Organization, headed by Yasser Arafat, agreed at a meeting last night to "Begin" implementation of this agreement. It did not say when. Up to now, the Palestinians have insisted on a "balanced formula" under which their withdrawal will occur simultaneously with the pullout of the Christian rightists and the entry of the Lebanese army into the area.

An estimated 5,000 Palestinians remain dug in around the towns of Khiam, Ibl al Saki, Taibe and Bint Jbail. Under the cease-fire agreement, most of them are to pull out of the border area and return to their camps elsewhere in Lebanon. Authoritative sources say the agreement as interpreted by Israel and the United States permits them to keep only about 500 men in the southeastern hills known as the Arquob.

The Palestinians, meanwhile, dispute that the agreement imposes any limit on the number of guerrillas they can keep in the Arquob, according to PLO sources.

The Christians, for their part, refuse to move out of the enclaves, where they have access to their allies in Israel. They claim that their fighters are in fact part of the regular Lebanese army sent to the south by its former commander, and thus are entitled to stay there to be reintegrated into the new national army when it moves south.

In addition, the Christian political leadership is accusing the Palestinians of reinforcing their troops in the south, rather than preparing to move out.

Camille Chamoun, the former president who remains one of the most powerful Christian leaders, said in an interview that "the Palestinians never honor any agreement. They are still in the south and they are increasing. President Sarkis tried to get me to share his optimism, but I am not optimistic." He and other Christian leaders have said that full Palestinian withdrawal from the south must precede any other moves.

Another thorny issue is the fate of the Lebanese fighters on both sides, Moslem and Christian, who originally were members of the Lebanese national army before it disintegrated during the civil war. Gen. Victor Khoury, the army's new commander, wants to take many of these troops back in as he seeks to reconstruct the armed forces.

Lebanese Moslem leftists, Palestinians and Syrians insist that the Christians in the south are so tainted by their alliance with Israel that no Arab nation can have them in its military ranks.

The Christians take the view that they are Lebanese and entitled to be in the army, and their alliance with Israel was forced on them by the Palestinians, outsiders who must go.

Maj. Saad Haddad, commander of the Christian forces entrenched around the town of Marjayoun, told reporters who visited him from the Israeli sdie that the troops of the national army who are coming in will reinforce, not replace, his forces.

According to sources close to the negotiations, this view has been [WORD ILLEGIBLE] the Americans. The United States is involved because it mediated the cepted by Sarkis, Khoury, the Israelis cease-fire and its diplomats here, in Tel Aviv and in Damascus are acting as a conduit for messages from the Israelis to the Palestinians and Syrians.

Until recently, Lebanon and Israel were negotiating directly, apparently through the forum of the Lebanese-Israeli mixed armistice commission, which has existed since 1949. Israel broke off these talks, claiming violations of the cease-fire, and in the past two days it has been U.S. Ambassador Richard Parker who has been meeting with Sarkis and other Lebanese officials.

According to informed diplomatic sources, the United States, Israel and the Sarkis government have taken the pisition that Haddad's Christian troops were in fact sent to the south originally on orders from Khoury's predecessor and are thus entitled to remain as part of the new force. Haddad himself is understood to have been told that he will have to go, because he accepted an Israeli decoration, but Chamoun and his allies have reportedly agreed to that.

Khoury also plans to take back into the army some troops who recently have been fighting on the side of the Palestinians in the south, Moslem soldiers of the Lebanese Arab Army, which broke away from the central command during the civil war.