JERUSALEM - Firing missiles, tank shells and machine guns at Palestinian Authority positions, Israeli troops killed 16 Palestinians yesterday in reprisals for a Palestinian shooting ambush that killed six Israeli soldiers - one of the deadliest attacks on Israeli troops in 17 months of fighting.

After nightfall yesterday, Israeli F-16 warplanes fired three missiles at a Palestinian police compound in Gaza, target of air strikes the night before, witnesses said. The Israeli military had no immediate comment.

The six soldiers were killed at a West Bank checkpoint, shot at close range by three militiamen linked to Palestinian leader Yasser Arafat's Fatah movement.

The ambush ignited debate on the military's tactics, including the effectiveness of checkpoints, and intensified pressure on Prime Minister Ariel Sharon to take more decisive action in stopping Palestinian attacks. "It's clear that the strategy that we've had until now can't continue," said the Israeli president, Moshe Katsav.

Sharon declared after a meeting of Israel's security Cabinet yesterday that he would embark on a "different course of action." He did not elaborate, but an aide, Raanan Gissin, said Israeli troops would switch from larger operations to quick, smaller-scale strikes intended to "tip the terrorists off balance."

Gissin also suggested the military would tighten its siege of Arafat's compound in Ramallah and prevent him from receiving foreign dignitaries, something he had been able to do until now. "If he (Arafat) stops the terrorist activities, if he gives the right order, he can meet anyone in the world that he wants," Gissin said.

In earlier reprisals by air, land and sea, Israel fired missiles at Arafat's seaside compound in Gaza City and his headquarters in the West Bank town of Ramallah. Arafat remained in his Ramallah office, the lights turned off and accompanied by a few close aides, said one of his advisers, Ahmed Abel Rahman.

A defiant Arafat later said that "neither tanks nor planes can scare us, they won't prevent us from achieving our demands," and he urged President Bush to intervene. An Israeli Foreign Ministry official, Gideon Meir, said Israel would respond to "this terror campaign which was imposed on us ... by Yasser Arafat and his gang."

In all, 16 Palestinians were killed, according to Palestinian officials: four in a missile attack on Arafat's Gaza compound, seven in Israeli shelling of two Palestinian police checkpoints near the West Bank town of Nablus, three in a firefight outside the Balata refugee camp close to Nablus, one in an airstrike on a Palestinian police post in the town of Ramallah, and one in a firefight near Ramallah.

The Palestinian dead included 12 policemen.

The past week has been one of the bloodiest since fighting began in September 2000. Seventeen Israelis were killed, including 13 soldiers, a policeman and three civilians. In the same period, 45 Palestinians were killed, including nine civilians, 22 members of the security forces and 12 assailants and suspected militants.

The ambush on the soldiers was carried out at about 9 p.m. Tuesday at an Israeli military checkpoint near the village of Ein Arik, west of Ramallah. The post was manned by eight soldiers who had arrived just several hours earlier for a tour of duty. A leader of the Al Aqsa Brigades - a Fatah-affiliated militia that claimed responsibility for the ambush - said the gunmen had carefully watched the checkpoint before the attack.

The Israeli army commander in the West Bank, Brig. Gen. Gershon Yitzhak, said the gunmen approached on foot, as though they were laborers returning home. They whipped out their weapons and killed three soldiers at the checkpoint, Yitzhak said.

One assailant then ran toward a nearby trailer that served as sleeping quarters and killed three more soldiers in their beds, the commander said. A soldier at a lookout was in shock and didn't fire back, but there was evidence that two other soldiers returned fire, Yitzhak said.

A Fatah leader in the West Bank, Marwan Barghouti, said such attacks are "the only way for the Israelis to understand that they should put an end to their occupation."

The three gunmen made a video ahead of the attack, explaining their motives, as is customary in what are considered suicide missions - though it would not be released since the gunmen survived and escaped, members of the Al Aqsa Brigades said.

Palestinians close to the militant groups said privately that the ambush was a sign of a switch in tactics. Assailants would largely focus on Israeli targets in the West Bank and Gaza, rather than inside Israel, believing that such attacks would give the Palestinians greater legitimacy in the eyes of the international community.

In the past few months, the Islamic militant Hamas and Islamic Jihad groups, as well as Fatah, have carried out deadly attacks in Israel, and it was not immediately clear if all militants supported the apparent switch in tactics.

Israeli military commentators sharply criticized the army's performance. "In the killing fields of the intefadeh (Arabic for Palestinian uprising), Israeli soldiers have gone from being the hunters to being hunted. Sitting ducks," wrote commentator Alex Fishman in the Yediot Ahronot daily.

Israeli troops displayed extra caution yesterday. At one barrier, a soldier asked two Palestinian paramedics approaching in an ambulance to get out at a safe distance and lift up their jackets to show they were unarmed.

Israeli reprisals began around 3 a.m. yesterday.

In the Gaza Strip, Israeli F-16 warplanes bombed a four-story police compound, razing the building and sending debris and shrapnel flying in all directions.

For the first time in 17 months, Israel attacked Arafat's seaside compound. Navy vessels fired missiles at the complex, punching holes into one of the walls, killing four guards and wounding eight.

Palestinians in nearby buildings fled in panic and hundreds remained in the streets, fearing their buildings would be hit.

Palestinians counted at least 40 explosions in the Gaza City raids.

In Ramallah in the West Bank, helicopter gunships fired a missile at a trailer serving as sleeping quarters for policemen in Arafat's compound. The officers had left the trailer in anticipation of an Israeli strike, but the blast blew out several windows in the complex.

Elsewhere in Ramallah, a Palestinian policeman was killed in a missile attack on his post and a gunman died in a firefight with Israeli troops west of the city.

Near Nablus, Israeli troops fired heavy machine guns and tank shells at two Palestinian police posts, Palestinian security officials said. Six policemen were killed in one attack, and one was killed in a second strike.

South of Nablus, Israeli tanks moved close to the Balata refugee camp. Three Palestinians, including a gunman, were killed in separate firefights, doctors said.