To outsiders, this Jewish settlement clinging to a hill in the northern West Bank would seem to offer a precarious existence.

Surrounded by Palestinian villages and near one of the largest Palestinian cities, Nablus, with a population of more than 120,000, Itamar has about 1,000 residents, many of them children or transient students studying at its religious academies.

The community’s vulnerability was brutally exposed Friday night when two infiltrators, widely thought to be local Palestinians, traversed the settlement’s perimeter fence, waited patiently for lights out, then, after finding the next-door house empty, slipped into the Fogel family’s home. They stabbed five members of the family to death in their beds: the parents, Udi, 36, and Ruth, 35, and three of their children, Yoav, 11, Elad, 4, and Hadas, a baby girl of 3 months.

By Tuesday, the assailants were still at large.

This was not the first attack in Itamar. In 2002, Rachel Shabo and three of her children were shot dead in their home by a Palestinian, along with a neighbor who came to their aid. A few weeks earlier, three students at the seminary were shot dead while playing basketball. Altogether, 20 residents have been killed in attacks since the settlement was established in 1984.

But with a kind of inverse logic, residents here say that with each bloody attack, their deeply religious and ideological community, though heartbroken, is also strengthened. Here, in the thick of the Israeli-Palestinian conflict, where the contest over the land is a daily reality, tragedy spurs greater commitment to the cause.

“Everywhere in the Land of Israel there are challenges,” said Michal Caspi, 26, the mother of a 5-month-old, who lives a few doors from the Fogel home. “The Land of Israel is a place where you have to invest.”

Nissim Edan, a farmer who has lived here for 21 years, said: “At the time of the first attack, there were 30 families here. Now there are 200.”

Within the close-knit community, residents seemed to have been lulled into a sense of security by the last few years of relative quiet. In the row of modest one-story houses where the Fogels lived, on the settlement’s edge, doors were often left unlocked. Bicycles and tricycles, balls and infants’ car seats are still left out on porches and lawns.

On Tuesday, Itamar was a hive of activity. Workers from a nearby settlement were retiling a porch a few houses from the Fogels’. On a rise across the street, students from one of the high school seminaries were cleaning up a playground and planting flowers.

On a hill beyond the perimeter fence, about halfway between Itamar and Awarta, the Palestinian village where the Israeli military was focusing its hunt for the killers, two prefabricated huts and a tent sprang up Saturday night, after the Sabbath.

On Tuesday, a bulldozer was carving a road through orchards and fields to link Itamar and the new unauthorized outpost. Three families, one from Itamar and two from the Gilad Farm outpost, were planning to sleep there at night.

“This is not the answer, it is just a beginning,” said one of the new outpost residents, who asked not to be named, as the construction was not legally sanctioned by Israel. “We are here to show that we go beyond the fence,” he said, “and to show the Arabs that we are not afraid.”

In this area, part of the territory occupied by Israel after the 1967 war, the friction between Israelis and Palestinians has often turned bloody. A year ago, two Palestinian teenagers were shot dead by Israeli forces in a nearby village during a confrontation. The next day, two Palestinian youths from Awarta, cousins age 18, were shot dead by Israeli soldiers in unclear circumstances.

The Jews who have settled in this area consider themselves the guardians of Nablus, or biblical Shechem. While most of the world considers the settlements a violation of international law, many in Itamar speak of this land as their God-given birthright.

“We have a legitimate right to the Land of Israel,” said Moshe Goldsmith, 47, the mayor of Itamar. “The Bible is our deed.”

Itamar started with 12 families in a cluster of prefabricated houses. Its outposts have since spread over a string of hills. Now, Mr. Goldsmith says, it covers a land mass the size of the Israeli coastal city of Netanya.

The biggest threat to Itamar’s existence would probably come from an Israeli government that decided to withdraw from the West Bank.

The Fogels moved to Itamar two years ago after a period in the large urban settlement of Ariel. They went to Ariel after being evacuated from Netzarim, a settlement in Gaza, when Israel unilaterally withdrew from that territory in 2005.

The growth of the isolated West Bank settlements, like Itamar, put Israel in a bind. They were created after the rightist Likud Party came to power in 1977 as a means of guaranteeing Israeli control of the land.

But the current prime minister, Benjamin Netanyahu, a Likud member, has endorsed the two-state solution in principle, meaning the partition of the land and the establishment of a Palestinian state alongside Israel.

That would most likely involve Itamar’s removal.

Mr. Goldsmith said that the settlement would not be able to go against the government. But he added: “An agreement that requires us to leave Itamar would be immoral. We believe that it will not happen.”

On Tuesday morning, many of the residents attended a newborn’s naming and circumcision. The baby was given the name Yair, which contains the Hebrew initials of four of those who were slain. Amid the grief, there was rejoicing at Itamar’s latest addition.