A Palestinian suicide bomber walked into a crowded Jerusalem pizzeria at lunchtime today and detonated a large explosive device packed with nails, police said, killing at least 14 others and injuring more than 100 people. It was one of the deadliest terrorist attacks in the city in years.

Six of the dead and many of the wounded were Israeli children or teenagers jammed into the Sbarro Italian restaurant at downtown Jerusalem's busiest intersection. Five were in critical condition and were fighting for their lives; 10 others suffered severe injuries.

At one instant, the pizzeria was sun-soaked, bright and cheerful -- thronged with families, babies in strollers, boisterous teenagers, a woman in her eighth month of pregnancy, a mother cutting pizza into bite-size bits for her toddler daughter. At the next, at 2 p.m., it was a horrifying tableau of death, body parts, blood, shattered glass and hysteria.

"There were wounded people, blood everywhere. The whole restaurant was in pieces," said Aaron Lerch, 22, a volunteer medic.

One of those killed in the blast was an American from New Jersey, Judith Greenbaum. Four Americans were injured, including a 3-year-old girl and her mother, who was reportedly in critical condition tonight.

[Before dawn Friday, Israel retaliated on two fronts. In the West Bank city of Ramallah, Israeli F-16 fighters fired missiles at a Palestinian police station, according to Palestinian sources quoted by news agencies. There was no immediate report of casualties, but the police station was said to be in flames.

[Israeli police also sealed off Orient House, the East Jerusalem headquarters of the Palestine Liberation Organization and the most prominent symbol of Palestinian presence in the city for years.]

The death toll in today's bombing was variously reported as low as 13 and as high as 19. The higher figure would make it the bloodiest attack in Jerusalem since March 1996, when more than 20 people were killed on a crowded bus by a suicide bomber. Along with a suicide bombing at a Tel Aviv disco June 1, which killed the bomber and 21 youths, today's attack was one of the most lethal acts of violence in the current Palestinian uprising, which began in September.

The militant Palestinian group Hamas claimed responsibility for the attack and threatened more to come. Hamas, also known as the Islamic Resistance Movement, said the bomber was Izzedin Masri, 23, from a village near the West Bank town of Jenin.

Elsewhere today, an Israeli girl, 17-year-old Eliza Malka, was killed in a roadside ambush as she drove with relatives near Jenin. Three other teenage girls in the car were injured, one seriously. Since fighting began, about 500 Palestinians and 150 Israelis have been killed.

Israeli Prime Minister Ariel Sharon huddled with his defense minister, Binyamin Ben-Eliezer, and called an emergency meeting late this evening of his security cabinet to consider a military response. Furious Israeli officials blamed Palestinian leader Yasser Arafat for the bombing, which they said his security forces did nothing to prevent.

"We're not playing games, we're dealing with murderers, and Israel has to do what's necessary to protect its citizens," said Daniel Seaman, a government spokesman. "What fault was there of the children who went to a pizzeria? What actions did they take that they deserved to die for?"

Transportation Minister Ephraim Sneh, a former deputy defense minister, said: "The natural reaction is rage, fury and anger. . . . But if we respond, the response should not be just a spectacular action, a futile action. We have to be effective and precise, and if there is no obtainable clear target of terrorists, it's better to wait."

Bracing for an Israeli reprisal, Palestinians evacuated ministries and security posts in the portions of the West Bank and Gaza Strip they control. Palestinian hospitals summoned extra nurses and surgeons to prepare for the worst, and Arafat, apparently fearing he has become a potential target, canceled a meeting with Islamic and other political factions in his West Bank office in Ramallah.

"Most of the streets in downtown Gaza City are emptied out," Palestinian journalist Saud Abu Ramadan said by telephone a few hours after the bombing. "It looks like a graveyard -- even the stores are shut down."

Arafat, after receiving a telephone call from Secretary of State Colin L. Powell, condemned the bombing and called for a joint Israeli-Palestinian cease-fire starting Friday. Israel rejected the proposal.

Palestinian officials said Israel had provoked the bombing by intensifying its campaign of assassinating prominent Palestinian militants. In particular, they cited the Israeli gunship missile strike last week against two senior leaders of Hamas, which left six other people dead, including two Palestinian children.

"We believe Sharon alone is responsible for the cycle of violence," Yasser Abed Rabbo, the Palestinian information minister, told Abu Dhabi Television. "In the past week at least 27 Palestinians were martyred [killed] in the policy of assassination and terror officially adopted by the Israeli government and justified by the American administration."

Marwan Barghouti, a senior West Bank political leader who was nearly hit in an Israeli missile strike last weekend, said attacks like today's are "the only way to end the [Israeli] occupation of Palestinian territories. This is a decision that the whole Palestinian people agrees on."

Recent polls suggest that three-quarters of Palestinians support suicide bombings inside Israel, and their sympathy for the bombers seems to have grown as Israel has pressed its policy of "targeted killings" directed at militant leaders. Israeli television broadcast footage this evening of Palestinian boys in the West Bank city of Hebron singing and chanting to celebrate the suicide bomber's success.

One witness in Jerusalem today said he believed the bomber had been dropped off at the restaurant, at Jaffa and King George streets, by a motorcyclist who then sped away. Police estimated the bomb weighed at least 10 pounds. They said the blast's intensity was magnified because the doors and windows of Sbarro, part of a New York-based chain, were closed to contain the air conditioning.

The explosion sprayed shards from the pizzeria's plate-glass windows in all directions, showering and cutting customers as well as petrified pedestrians at the crosswalk outside. Witnesses said some people were thrown 10 yards by the shock wave.

"I heard a huge boom, and I saw my mother was hurt," said Haya Mizrachi, a woman in her mid-twenties, her voice shaking. "I brought her water. Her leg was covered in blood, and someone else there had fainted. . . . I can't believe this is happening in our country. Maybe what we really really need is a policeman at every corner."

The slain American, identified by officials as Judith Greenbaum, 31, but whose family called her Shoshana, was in Israel for a six-week study program. She had been working on a master's degree in education at Yeshiva University in New York. Greenbaum, who was pregnant, and was due in February, was scheduled to return to her home in New Jersey next week.

Greenbaum's father, Alan Hayman, said from his home in Los Angeles that the pizzeria "was one of her favorite places to eat in Jerusalem. She had been there many times before."

Greenbaum's husband, Steven, left tonight for funeral services in Israel, Hayman said.

When word of the bombing reached the family, Hayman said, he and his wife started furiously making calls to find their daughter.

"She was our only child and this would have been our first grandchild," he said.

The injured, who were rushed to three area hospitals, suffered "blast wounds, burns, shrapnel wounds, fractures, combinations of all these, neurological damage, head trauma," said Floru Sharon, emergency chief at Bikur Holim Hospital, about 100 yards from the site of the explosion.

Chaim Yavin, a medic, told Israeli television: "The scene was horrific, like after a battle -- parents were looking for their children and children were looking for their parents. I don't remember an attack with so many children hurt."

The bombing of the pizzeria followed a rash of warnings from Israel's security agencies that a major terrorist attack in Jerusalem was imminent, as well as a number of attempted bombing attacks thwarted by Israeli forces. The alerts had intensified since July 31, when an Israeli helicopter gunship attack killed Jamal Mansour, the top-ranking Hamas leader in the West Bank, and his deputy, Jamal Salim, in the city of Nablus. After those killings, Hamas vowed to take revenge.

"These assassinations don't work," Danny Rubinstein, an Israeli journalist who covers Palestinian affairs for the Haaretz newspaper, told Israeli television. "This [suicide bomber] is from Jenin, and many of the assassinations we've carried out have been in Jenin. This is the bitter truth."

But other Israelis insisted that only tougher action would work. "Terror can be defeated only . . . by intensive military pressure on the Palestinian Authority itself," said Yuval Steinitz, a hard-line lawmaker from Sharon's Likud Party.

Israelis were stunned by the attack today and furious that the target was an eatery frequented mainly by families, children and teenagers. Many said negotiations with the Palestinians were clearly useless and that Israel had to win an outright military victory.

"That's why we maintain a large army, to have a military solution for these things," said Raphi Pollack, 43, an obstetrician-gynecologist who treated some of those wounded in the bombing. "If not, we can scale back the army and have a large Foreign Ministry, and that way I don't have to pay 60 percent of my income in taxes."

Not far from Sbarro, news of the bombing provoked Jews to attack Arabs on the street at downtown Jerusalem's Mahane Yehuda outdoor produce market, which has also been the target of Palestinian terror attacks in the past. Police said they rushed there to intervene.

Jerusalem Mayor Ehud Olmert said Israeli security forces had prevented many recent attacks inside Israel but simply could not thwart all of them. He urged Jerusalem residents to go on with their lives as normal, and he rejected suggestions that people be warned to avoid downtown.

"How can we do it?" he said. "Do you know how many warnings we receive each day? How can people be expected to live like that?"

Staff writers Christine Haughney in New York and Clarence Williams in Washington contributed to this report.

Israeli police and medics scour the wreckage at a restaurant in the heart of downtown Jerusalem, where a Palestinian bomber killed himself and at least 14 other people. Judith Greenbaum of New Jersey, shown with husband Steven last year, was killed in the restaurant bombing in Jerusalem. Izzedin Masri, 23, right, was identified by the militant Palestinian group Hamas as the suicide bomber.