Israeli-supported Christian militias opened heavy machine gun fire on a Norwegian unit of the U.N. peacekeeping force yesterday, triggering an hour-long shootout, local residents reported.

Residents said the Norwegians came under fire at Khreibeh, four miles southeast of the rightist enclave of Marjayoun, and that the Norwegians returned the fire.

There were no U.N. casualties reported.

The rightists also shelled the nearby town of Rashaya el Fukhar, injuring three villagers, the residents said.

The shootout came less than 24 hours after an announcement in Israel that the rightist militias had agreed to allow the United Nations free movement in southern border areas now under their control.

The announcement said the rightists would allow the peacekeeping forces to man observation posts along the Lebanese-Israeli border and open offices in Marjayoun and Bint Jbeil.

Meanwhile, a fleet of Israeli vessels carried out maneuvers off the southern Lebanese coast this week, a Palestinian spokesman said.

In the north, a right wing newspaper reported that villagers in the town of Bcherri, 64 miles northeast of Beirut, had begun taking their heavy weapons out of storage following the slaying of eight civilians, allegedly by Syrian troops, near the famed "Cedars of Lebanon" National Forest earlier this week.