Shiite Amal militiamen battled Palestinian fighters in the densely populated refugee camp of Burj al Barajinah for the fourth straight day after night-long street fighting between Moslem militias in west Beirut.

Ghassan Seblani, a leader of the Shiite Amal movement, confirmed reports that an irate Shiite gunman, enraged by the killing of his brother, an Amal fighter, had stormed the homes of Palestinians in the Haret Hraik suburb southeast of Beirut yesterday, killing at least 14 persons.

The latest round of Shiite-Palestinian fighting, now in its fourth day, has raised fears of a second chapter of bloody warfare pitting Amal against Palestinian guerrillas entrenched in the refugee camps around Beirut, such as took place in May and June. Reports of arms deliveries into Burj al Barajinah, a maze of narrow streets and tightly packed block houses that Amal failed to storm earlier in the summer, have fueled fears of a prolonged battle.

The first round of fighting in the camps claimed more than 650 lives and wounded 2,500. It ended with a Syrian-sponsored cease-fire and brought Syrian military observers to Beirut as part of a multiparty coordination committee to supervise the truce. Attacks by Shiite Amal militiamen against wounded Palestinian fighters and civilians drew heavy criticism in June from Sunni Moslem politicians and Moslem clergymen.

At least 40 persons were killed and 80 wounded in the past 36 hours. The fighting in the camps led to the diversion of traffic from the main road leading to the Beirut airport.

Speaking of the attack on Palestinians in Haret Hraik, Seblani said: "We have to admit that it was done. The man who did it is not a member of Amal, but the severest punishment will be taken against him." Speaking after a meeting of Amal's leaders, Seblani explained that the unnamed Shiite man had retaliated in an "uncontrolled fit" for the death of his brother.

"His actions were against Palestinian civilians, not fighters. And it is our responsibility to protect them," Seblani added.

Seblani's comment blaming the attack on a disturbed individual came after the Marxist-oriented Democratic Front for the Liberation of Palestine had accused Amal of storming a number of buildings in Haret Hraik and liquidating "Palestinians living there in one batch, then dumping them in the street." The statement said at least 17 persons were killed, including some who took refuge in a nearby office of the National Syrian Socialist Party.

Seblani also said Amal's Politburo decided tonight to enforce a cease-fire and dispatched some of its members to help put it into effect. He added that an "emergency commission has been formed to try all those responsible for the latest outbreak and to carry out punishments against violators."

Last night, Druze fighters of the Progressive Socialist Party battled Amal militiamen following an argument over gasoline rations and the right of way in a Moslem neighborhood. The clashes spread as Moslem gunmen poured into the streets and fought with rocket-propelled grenades and machine guns from alleys and roofs.

Amal officials said tonight they were doing their best to put an end to the fighting in Burj al Barajinah. A Palestinian spokesman said the camp's military committee had decided on a "collective response" to the actions of Amal and the Lebanese Army 6th Brigade backing it. He said Amal was using 60-mm, 80-mm and 120-mm mortars against the camp.