Jerusalem ? In a major policy change, Israel will seize and reoccupy Palestinian lands until “acts of terror” against its civilians end, the government said early today, responding to a suicide bombing that killed 19 bus passengers and wounded 55 others.

Shortly after the announcement, Israeli tanks and troops invaded the West Bank city of Nablus and arrested three suspects, then withdrew. Troops also moved into Jenin and its refugee camp, and the town of Qalqiliya. Soldiers arrested six Palestinians in the city of Hebron and two nearby villages.

Police bomb disposal experts work in and near a bombed bus in Jerusalem. During morning rush hour Tuesday, a suicide bomber blew up on a crowded city bus in Jerusalem, killing at least 19 people and wounding 55, police said.

Tuesday’s attack by a Palestinian who exploded a nail-studded bomb was the deadliest in Jerusalem in six years and the 70th suicide attack since the current round of violence erupted nearly two years ago.

The Israeli government answered with an important policy statement, saying it was changing its response to “murderous acts of terror.”

The statement, announced after late-night consultations between Prime Minister Ariel Sharon and his top Cabinet ministers, said Israel will capture Palestinian Authority territory. “These areas will be held by Israel as long as terror continues. … Additional acts of terror will lead to taking of additional areas.”

The White House said it had no immediate comment on Israel’s decision. And it wasn’t known what impact, if any, it would have on a planned major Mideast policy address later this week by President Bush. He was expected to propose establishing a “provisional” Palestinian state in part of the West Bank and Gaza without deciding on its final borders and while neither side has embraced the idea, there is some hope that a renewed and forceful U.S. diplomatic drive might help end 21 months of carnage and despair.

Sharon questioned Palestinian leader Yasser Arafat’s ability to run such an independent state, saying, “It is interesting to know what kind of Palestinian state they mean.”

Unlike earlier statements, the Israeli government today did not characterize its planned incursions as short-term. Even a six-week invasion in late March, Israel’s largest military operation in two decades, was described as limited to destruction of terror capabilities, not holding on to territories.

Hours after Tuesday’s blast, an angry Sharon strode past a row of victims in body bags and peered into the bombed-out bus, vowing to retaliate. Two students were among the dead and four were among dozens wounded in the attack.

The Palestinian Authority condemned the attack. But the Palestinian leadership has not appeared ready to act decisively against radical groups, as Israel has demanded.

In Ramallah, Palestinians anticipating an army invasion and extended curfew began hoarding food.

Israeli Prime Minister Ariel Sharon, surrounded by police and security, looks toward a row of dead in body bags at the site of the suicide bombing.

“The Israeli response usually is against the Palestinian people, the Palestinian president and the Palestinian Authority,” said Labor Minister Ghassan Khatib. “It will not be any surprise if they decide to invade Ramallah again or impose a new siege on the president.”

In Washington, the White House said Bush condemned the bombing “in the strongest possible terms,” but aides wouldn’t say if it would delay his policy statement, expected today.

Bush has been formulating his approach to Mideast peace for weeks, during which he has met with Sharon, Egyptian President Hosni Mubarak, Saudi Crown Prince Abdullah and senior Palestinian officials.

The nail-studded bomb tore through the bus as it waited at a crowded intersection just before 8 a.m., sending bodies flying through windows and peeling off the roof and sides.

The Islamic fundamentalist group Hamas identified the assailant as Mohammed al-Ghoul, 22, a graduate student in Islamic studies from the Al Faraa refugee camp in the West Bank. Al-Ghoul left behind a farewell note in which he said he’d tried twice before to stage attacks.

“This time, I hope I will be able to do it,” he wrote. “How beautiful it is to make my bomb shrapnel kill the enemy.”

Inside a religious school a few hundred yards from the blast, 15-year-old Shmuel Calfon was praying with other students when they heard the explosion.

“Everyone looked at each other and thought, ‘That was an attack.’ But I didn’t want to be the one to say it,” Calfon said. Soon, sirens wailed and students began shouting and calling home to assure worried parents.

Police had been on high alert since Monday after receiving warnings that suicide bombers were trying to carry out an attack in Jerusalem.

There have been some 70 suicide bombings in 21 months.