SIDON, Lebanon (AP) _ Iranian-backed Shiite Moslem guerrillas outnumbered 2-to-1 drove back a three-pronged assault on their south Lebanon mountain stronghold today in fierce fighting with pro-Syrian rivals.

Police said a 1,000-strong force from the mainstream Shiite Amal militia lost five fighters killed and seven wounded in the failed attack against fundamentalist Hezbollah members entrenched in Jbaa village southeast of Sidon.

The new casualties brought the overall toll to 112 killed and 227 wounded in five days of savage fighting in Jbaa's Iklim el-Tiffah, or Apple Province.

The spokesman, who cannot be named in line with police rules, said casualty figures were not available for the 500-strong Hezbollah force trapped in a 9- square-mile triangle on the western edge of Israel's self-proclaimed security zone in south Lebanon.

At least 141 people, including civilians, have been killed and 307 wounded since the latest round of inter-Shiite hostilities broke out Dec. 31 in Beirut and south Lebanon.

The police spokesman said Amal fighters attacking from the west, southwest and south reached the outskirts of Jbaa, 10 miles southeast of Sidon ''but were pushed back in fierce fighting.''

He said the Amal militiamen withdrew in tanks and armored personnel carriers behind heavy artillery cover to nearby Kfar Filla, Ein Qana and Jarjou villages.

An Amal commander in Sidon, identified only as Abu Jamal, blamed the steep terrain for the setback.

''Jbaa is a mountain peak. Our fighters are in the valleys and we have to climb up to the Hezbollahis. This is not an easy task,'' he said.

Abu Jamal said his forces intended to starve out the Hezbollah force after cutting off supply lines to their redoubt that stretches southeast from Jbaa to the nearby hamlets of Ein Bouswar and Louwaizeh and the wooded slopes of Mount Safi.

''We'll besiege them for a while, until they run out of supplies and ammunition and then try again ... We don't want to sacrifice our fighters in a battle that we can win easily after a while,'' he said.

Amal, Arabic for hope, and Hezbollah, which means Party of God, are fighting for control of Lebanon's 1-million-strong Shiite community, the largest religious group in a country splintered by 13 years of civil war.

Hezbollah aims at setting up an Islamic state in Lebanon, patterned on Ayatollah Ruhollah Khomeini's regime in Iran.

The more secular Amal rejects Iran's spiritual influence over Lebanese Shiites and favors a multi-sect government where Moslems and Christian share power equally.

Police said both sides have committed ''horrific atrocities'' in this week's fighting and that several victims were found with their heads cut off.

The current battle is the fourth major confrontation between the two factions since Amal cracked down on Hezbollah last April in most of southern Lebanon. A month later Hezbollah retaliated by ousting Amal from most of south Beirut in three weeks of bloody clashes.

Syria deployed troops in south Beirut in an effort to contain the fighting but more battles erupted in November and spread to west Beirut.

According to police, 388 people were killed and 1,203 wounded in the previous three rounds of fighting in south Lebanon, south and west Beirut.

Syria, which considers Lebanon part of its sphere of influence, now has more than 40,000 troops in eastern and northern Lebanon as well as in west and south Beirut.