BEIRUT, Lebanon (AP) _ Palestinian factions fought with mortars and machine guns in Beirut's refugee camps Monday, and Shiite Moslem clans battled each other in neighboring slums. Police said 19 people were killed and 68 wounded.

Lebanon's Christian community was shaken by the discovery of the bullet- riddled body of a prominent Maronite Catholic priest five days after he was kidnapped from his home in Jounieh, a Christian port city.

Fighting in the Chatilla and Bourj el-Barajneh refugee camps pitted guerrillas of Palestine Liberation Organization chief Yasser Arafat's mainstream Fatah against Syrian-backed dissidents, police reported.

It was the first such battle since Arafat and President Hafez Assad of Syria took steps toward reconciliation last week in Damascus.

Police said they had no information on what caused the clash, which began Sunday night and continued Monday. Both sides used mortars, rocket-propell ed grenades and heavy machine guns.

Intense fighting kept reporters and photographers out of the area.

PLO spokesmen said Arafat's supporters overran three of the four main positions in Chatilla held by fighters of Col. Saeed Mousa's Fatah-Uprising faction.

At least eight combatants were killed and 43 others wounded in the two camps on Beirut's southern flank, the police report said.

A 50-man committee including members of several guerrilla factions and Lebanese Moslem groups was organized late Monday to try for a cease-fire, the police report said.

Eleven people were killed and 25 wounded in night-long fighting between two Shiite clans in the Raml el-Aali and Roweisse slums, police reported.

They said fighters of the Atat and Awad clans were battling for dominance in the two districts along the airport highway near Bourj el-Barajneh.

Justice Minister Nabih Berri's Amal militia, the main Shiite force, moved in after midnight to enforce a cease-fire.

An Amal statement ordered both clans to put down their arms and leave the streets, declaring that violators would be shot on sight, but sporadic sniping persisted Monday.

The 7,500 soldiers Syria deployed in Moslem west Beirut more than a year ago to stop factional fighting have not gone into the Shiite slums. Syria keeps about 25,000 soldiers in northern and eastern Lebanon and is the main power broker after 13 years of civil war.

Maronite bishops held a special meeting Monday and declared the slaying of Monsignor Albert Khreish a ''monstrous crime.''

A hunter found his body, which had at least 30 bullet wounds, in a pine forest Sunday near Ghazir, a mountain resort in the Christian hearland north of Beirut, police said.

Khreish, 53, head of the sect's religious affairs court and nephew of former Patriarch Antonios Butros Khreish, was kidnapped April 26.

His body was clad in pajamas and his face bore marks of physical torture, police said.

''The culprits deserve the excommunication punishment,'' said the statement issued after the bishops met at Bkirki, the home of Patriarch Nasrallah Sfeir about 12 miles north of Beirut.

Their reference to excommunication suggests the bishops believe Christians killed Khreish in a factional dispute. Police said they had no information about a possible motive.

Jounieh and Ghazir are controlled by the Lebanese Forces, the main Christian militia.

No mention of the militia was made in the bishops's statement. It urged Lebanon's president and army commander, both Maronites, to ''exert utmost efforts to find the murderers and bring them to justice.''

The bishops expressed ''profound concern over worsening security conditions'' and said Khreish's murder was ''aimed at discrediting the church and its role in Lebanon.''

Funeral services were scheduled for Tuesday in Bkirki and burial will be at Ein Ibil, the priest's hometown in the ''security zone'' Israel maintains just north of its burder with Lebanon.