Iran seems to be hurtling toward nuclear weapons capacity, Hezbollah could win Sunday’s election in Lebanon and Hamas is smuggling long-range rockets into Gaza again. So why is President Obama focusing such attention on the building of homes by Israeli Jews in the West Bank?

That, in essence, is the question being angrily posed by the Israeli government of Prime Minister Benjamin Netanyahu and underscores one of the biggest shifts in American policy toward the Israeli-Palestinian conflict in three decades. While every administration has objected to Israeli settlement building in occupied lands, the Obama administration has selected it as the opening issue that could begin to untie the Gordian knot of the conflict.

American officials hope that by getting Israel to freeze settlement building on land where the Palestinians expect to build their future state, they can then press Saudi Arabia and other regional powers to offer Israel concessions like low-level trade or tourism. In addition, stopping the construction would remove a major concern of the Palestinians that their land is slowly disappearing under settler housing. In his Cairo speech on Thursday, the president again called for an end to the settlement building.

“Obama may have found the soft underbelly of Israel, because ending settlements is a consensus issue in the world, among American Jewry and even among a majority of Israelis,” said Yossi Beilin, a former leftist minister and member of Parliament who now runs a private consulting firm. “He needs a strong regional coalition to leave Iraq — and not to leave it to Iran. And it seems like he sees ending settlements as a way to start this process. The only question is whether Netanyahu can do what is needed.”

The administration is starting with settlements for two reasons. It wants to send a message to the Arab world that the previous eight years of siding consistently with Israel are over — hence the Cairo speech and the focus on improving relations with Muslims. And it is one place where it actually has leverage — given the American backing of Israel, it can push Israel to live up to its commitment far more easily than it can persuade Hamas to abandon violence.

A poll published in Friday’s Yediot Aharonot newspaper lends some credence to the view that most Israelis would be willing to go along. Asked whether Mr. Netanyahu should acquiesce to Mr. Obama’s demands or risk American sanctions, a small majority favored acquiescing. When asked whether Israel should freeze settlement construction, another slim majority agreed. But when asked about “natural growth” of families in the settlements, a majority favored making allowances.

The issue of natural growth has surfaced so prominently because while the Israeli government presents it as a simple humane need to make room for expanding families, the data show that settler growth has been enormous in recent years and nearly all of it has been labeled natural growth.

While stopping the bulldozers seems like a relatively easy request of Israel, it is politically dicey for Mr. Netanyahu and technically complicated. His governing coalition includes parties with right-wing constituencies whose central goal is to expand settlements. Moreover, 40 years of settlement building have created interlocking bureaucracies and constituencies that will be hard to stop.

As Yossi Verter, a political analyst, put it in the liberal newspaper Haaretz on Friday, Mr. Netanyahu “will have to decide over the coming weeks whom he would rather pick a fight with: the powerful American administration, whose president sees himself in an almost messianic role, or his own coalition and members of his party.”

Whether Mr. Netanyahu can do it and survive politically is not the only question here. A second is whether this new American approach holds any promise.

“I am not a Greater Israel guy and I have no objection to dismantling settlements as part of a peace deal, but getting so hung up on freezing settlement growth is not wise because it is not the most important issue out there,” argued Efraim Inbar, director of the Begin-Sadat Center for Strategic Studies at Bar Ilan University.

The far bigger concern, he said, is that the Palestinians are unable to make similar concessions because of their political divisions and weakness.

Israelis have turned rightward and most analyses suggest that the reason is a growing fear of regional threats, notably Iranian-backed parties like Hezbollah and Hamas, on Israel’s borders.

Sarah Honig, a columnist for The Jerusalem Post, a conservative paper, put it this way a week ago in a column: “Settlements aren’t the problem and removing them isn’t the solution. Israel foolishly dismantled 21 Gaza Strip settlements in 2005. Did peace blossom all over as a result? Precisely the reverse occurred. The razing of Israeli communities was regarded as terror’s triumph, expediting the Hamas takeover.”

The settlements are a complex issue that resonates in surprising ways here. Zionism began 125 years ago through the Jewish purchase of land in Palestine and the building of settlements on what the Jews saw as their ancient homeland. When Israel won additional territory in the 1967 war, a conflict it felt was imposed on it, many here viewed it as the miraculous continuation of Jewish national rebirth in the biblical heartland. Religious Jews began settling there, but others were attracted by low prices, open space and a pioneering ethos.

Criticism ensued immediately, including American government condemnation. The Fourth Geneva Convention forbids a country to settle its civilians in areas conquered militarily. Israel set up military outposts that turned into civilian settlements.

Palestinians were enraged. Some resorted to terrorism, leading some Israelis to argue that settlements were a vital front line to protect the heartland.

After Israel and the Palestine Liberation Organization agreed in 1993 to mutual recognition and began negotiating the terms of a Palestinian state, Israel ended construction of new settlements. But the boundaries of existing settlements were large, and over the next decade, the settler population more than doubled and now stands at nearly 300,000.

In 2003, Israel and the Palestinians signed the so-called road map for a two-state solution, calling on Israel to freeze all settlements, and on the Palestinians to dismantle terror networks. Neither has done so.

The Israelis say they had unwritten agreements with the Bush administration to continue building, as long as no new settlements were built. Bush officials say that is only partially true. The Obama administration says such winks and nods are over. It is signaling the Arab world that it is shifting policy. Whether it does so, and how the Netanyahu government responds, will make for high drama in the coming months.