Syrian troops and Lebanese rightist militia forces fought each other with mortars and rockets in Beirut tonight.

The right-wing Phalangist radio accused the Syrians of opening fire on Christian rightist positions. It said that Palestinian and Lebanese leftist forces had joined the fighting.

Rightist sources said they believed the death of a port worker, killed by sniper fire earlier today, sparked the fighting.

The battle was centered on the port area and the commercial district, main combat zones in the 1975-76 civil war that brought Syrian troops to Lebanon.

Red tracers criss-crossed the night sky and the area was lit up by the bright flashes of exploding shells. Reports of casualties were not immediately available.

About 30,00 Syrian troops are stationed in Lebanon under an Arab League mandate to keep the peace. The rightists, who draw their support from Lebanon's Christians, consider the Syrians an occupation army.

In southern Lebanon, the Palestine Liberation Organization accused Israeli gunners of intermittently shelling scattered locations in the coastal sector.

The PLO news agency WAFA said the Palestinan refugee camp of Rashidiyeh, 55 miles south of Beirut, came under an "Israeli artillery barrage as of noon Monday." The report said gunner also lobbed shells at scattered locations in the Tyre area. No casualties were reported.

Lebanese officials did not comment on the report.

The port city of Tyre, 50 miles south of Beirut, houses three Palestinian refugee camps on its southern, eastern and northern edges. Rashidiyeh camp has 13,000 Palestinian refugees registered with the United Nations Relief and Works Agency for Palestine Refugees.