Negotiations over the withdrawal of Palestine Liberation Organization guerrillas from Beirut have twisted and turned continually since July 3, when PLO leader Yasser Arafat signed a detailed document agreeing in principle to a PLO evacuation from Lebanon.

Mediators believed the Arafat document was a major breakthrough. But questions concerning how, when and to where the PLO would withdraw have continued to haunt the talks.

Arab nations first were reluctant to accept the PLO fighters. After persistent U.S. efforts, Syria, Jordan and Egypt agreed last month to accept a portion of the PLO under certain conditions.

There was disagreement over the timetable of the withdrawal. PLO officials said that while they could consent to a token evacuation of a small guerrilla unit, they insisted that Israeli forces withdraw from Beirut simultaneously with the main PLO evacuation and with the deployment of an international peace-keeping force. But Israeli officials say they will not withdraw until assured that the PLO has left the country.

Israel also expressed strong opposition to the PLO's insistence to retain a political office in Beirut and to leave behind two 250-man military units in Lebanon until Israeli and Syrian forces also left the country.

Israeli officials said nine days ago that U.S. envoy Philip C. Habib had promised to seek within two days a PLO commitment to leave. A day later, Arab League ministers meeting in Jeddah, Saudi Arabia, signed a statement committing the PLO to leave but Israel saw it only as delaying tactics.

Even during the intense attacks of the past week, progress in the negotiations was reported.