NABLUS, DEC. 11 -- Israeli soldiers today fired on Palestinian demonstrators at a refugee camp here, killing at least three people and raising the toll to at least six dead and more than 50 wounded over the past three days in the worst outbreak of violence in several years in the occupied West Bank and Gaza Strip.

Two of today's dead were 11-year-old boys, according to Arab witnesses at the Balata refugee camp. Their account of the incident differed widely from that of the Army. Of the Palestinians killed since Wednesday, two were teen-agers and three were 12 years old or under.

The shootings occurred after military authorities pledged to increase patrols and crack down on stone-throwers in the camp, which the Army considers a hotbed of Palestinian resistance. An Army spokeswoman said tonight that the tougher measures would continue despite today's deaths because "if we allow this to go on, it will spread all over" the West Bank.

{Four Arab guerrillas in a fishing vessel fired on an Israeli patrol boat off Lebanon Thursday night and killed an Israeli lieutenant before troops sank the vessel and killed all aboard, the Israeli Army said, according to The Associated Press.

{The pro-Iranian Islamic Resistance said in Lebanon that it was responsible for the clash and that its fighters had killed 35 Israeli sailors.}

The spokeswoman said today's incident here began when dozens of residents at the camp were ordered out of their houses by two rival youth gangs that dominate the area and surrounded a patrol of Israeli border police. "They began throwing every possible thing -- bottles, stones, metal," said the spokeswoman, who requested anonymity.

She said that three policemen were injured and that police fired rubber bullets and tear gas and used live ammunition only when their lives were endangered. She said three people were killed -- a boy, 12, and two women, 19 and 50 -- and seven wounded.

But Palestinian witnesses and staff members at Ittihad hospital said at least four people had been shot dead and 11 injured. Their list had the names of two 11-year-old boys, Mohammed Faor and Ali Abdullah; Sahad Jarmi, 17, and Suhaila Kabi, in her 50s.

The scene at the hospital tonight was one of pandemonium. While angry youths sought to erect makeshift barricades on the roads surrounding the hospital, anxious relatives filled the halls and rooms, crowding around doctors attempting to treat the wounded.

Arab witnesses charged that Palestinians at Balata have been harassed for several days by Druze border police who broke into homes and randomly beat residents of the camp, which has a population of about 11,000. They said the police assaulted young men emerging from noon prayers at a mosque today. When the men resisted, the police opened fire, they charged.

The Army then sealed off the camp and delayed ambulances that sought to remove the victims, according to drivers. Shots could still be heard from the camp at dusk, nearly five hours after the incident.

Israeli military authorities say they cannot explain the current violence, which began last weekend with the stabbing death of an Israeli businessman in Gaza City. It started up again Wednesday after an Israeli truck driver collided with two vans, killing four Gaza residents in an accident that Gazans charged was deliberate revenge.

Soldiers opened fire in four incidents in Gaza that day. The Army said one person was killed and 20 wounded; Gaza hospital authorities put the toll at two dead and 27 wounded. The next day Gaza erupted again, as did this West Bank city about 40 miles north of Jerusalem. Two youths were killed -- an 11-year-old resident of Gaza and a teen-ager here.

Unidentified military officials told the newspaper Haaretz yesterday that the Army has decided to pursue a tougher line against nationalists at Balata, scene of dozens of stone-throwing incidents this year. In the past, the authorities said, the Army avoided confrontations here but they said that policy had encouraged the two youth gangs -- one loyal to Fatah, the main branch of Yasser Arafat's Palestine Liberation Organization, the other to the rival Popular Front for the Liberation of Palestine.

"We are not going to leave any place under the control of any terrorist organization," the Army spokeswoman said. "It's not a change in policy, it's a change in tactics."

Recent events have helped inflame Palestinians, including last month's Arab League summit in Amman, Jordan, where the Palestinian issue was played down. A Palestinian commando attack that killed six Israeli soldiers in northern Israel two weeks ago also apparently inspired new resistance here.