BEIRUT, SEPT. 12 -- Palestinian guerrillas and Syrian-backed Shiite Moslem militiamen have agreed to end more than two years of sporadic fighting, newspapers reported today.

The Palestinians agreed to withdraw from positions they captured in southern Lebanon in return for peace with Shiites who had tried to block the resurgence of the Palestine Liberation Organization, the daily An Nahar said.

It said the agreement was reached during a meeting yesterday in Sidon, provincial capital of southern Lebanon, of senior officers from Amal, the dominant Syrian-backed Lebanese Shiite faction, and the PLO's main factions.

The meeting brought Amal and Fatah, the mainstream PLO faction, together for the first time since the Shiites launched their crackdown in May 1985 to halt the creation of a new PLO power base in Lebanon. The Palestinian guerrillas had left during the 1982 Israeli invasion.

A statement released at the end of the meeting, published by An Nahar and other newspapers, said the Palestinian guerrillas agreed to withdraw from strategic hilltop positions they captured last year east and southeast of Sidon.

In return, Amal would lift its siege of camps in Beirut.

The statement did not mention a deadline for implementing the accord, but An Nahar said the Palestinians were expected to begin their withdrawal to camps near Sidon on Oct. 5.