JERUSALEM — High up in an empty, mountainous expanse east of this city there is a stone patio with a pair of green metal benches and a plaque marking the cornerstone of a future Jewish community. Dedicated in 2009, the plaque promises the new city will be built “adjacent to the united Jerusalem, which will be quickly re-established.”

Jerusalem, which both Israel and the Palestinians see as their capital, is anything but united, with fierce fights over its development posing perhaps the greatest threat to the prospects of peace. And beyond the cornerstone, nothing has been erected since in this contentious 4.6-square-mile area, known as E1, where there are many more goats than people.

But Israel’s announcement on Friday that it was moving ahead with zoning and planning preparations for the area could change all that, and many fear that it could close the window on the chance for a two-state solution to the long-running Israeli-Palestinian conflict.

Construction in E1, in West Bank territory that Israel captured in the 1967 war, would connect the large Jewish settlement of Maale Adumim to Jerusalem, dividing the West Bank in two. The Palestinian cities of Ramallah and Bethlehem would be cut off from the capital, making the contiguous Palestinian state endorsed by the United Nations last week virtually impossible.

Although Israeli officials did not call the move retaliation for the United Nations vote, most people here assumed the timing was not coincidental.

“It’s like two 3-year-old children playing, and one is hitting and the other is slapping instead of sitting down,” said Alex Lash, 56, an Israeli who was having a breakfast at a bustling restaurant here on Saturday morning in the Palestinian neighborhood of Beit Hanina after a three-hour mountain-bike ride. “It’s a never-ending story: we are doing something, they are doing something, one movement brings the other side’s movement. There is no end for that.”

Zakaria al-Qaq, a professor of national security at Al Quds University here and a resident of the East Jerusalem neighborhood of Silwan, also described the situation as a hopeless “cycle of action and reaction,” and said that Prime Minister Benjamin Netanyahu was under pressure to act because of the Israeli elections on Jan. 22.

“Maybe the Palestinians got something on paper and morally, but he got something on the ground,” Mr. al-Qaq said. “Netanyahu is trying to enforce something on the ground and gain the hearts and minds of the Israeli public. It’s a strong message to the Palestinian leadership that Netanyahu is not without cards in his hand.”

The development of E1, a project that the United States has blocked several times since 1994, has long been seen as a diplomatic third rail, and several experts said Saturday that they expected that Israel may once again back down from building there. But several other controversial housing projects within Jerusalem have sped forward in recent months, raising the ire of the Palestinian leadership, left-leaning Israelis and the international community, most of whom see the settlements as a violation of international law.

Along with zoning and planning for E1, Israel on Thursday approved 3,000 new housing units in unspecified parts of East Jerusalem and the West Bank.

Dani Seidemann, a Jerusalem lawyer and longtime antisettlement activist, said that even before the latest decision, the government had issued tenders for the construction of 2,366 units in 2012, more than twice the number built in the previous three years combined.

These include more than 1,200 units in Ramot and Pisgat Zeev — decades-old upscale Jewish neighborhoods of 40,000-plus residents that straddle Beit Hanina in the northern reaches of the municipality. Late last month, final approval of 2,610 units in an undeveloped southern stretch known as Givat Hamatos was postponed under international pressure because it was scheduled while Secretary of State Hillary Rodham Clinton was in the region trying to negotiate an end to Israel’s bloody conflict with the Gaza Strip.

“Now approaching the point of no return,” Mr. Seidemann said during a tour of the area Saturday. “It’s the largest settlement surge in Jerusalem since the 1970s.”

Israel began building and expanding East Jerusalem in 1968, shortly after it wrested control of the area from Jordan. There were about 69,000 Palestinians living there then. Now, nearly 300,000 Palestinians and more than 190,000 Jews live in dozens of separate communities scattered throughout the areas north, east and south of the Old City that are collectively called East Jerusalem. (Some 2,500 Jews have also settled house by house in close-in neighborhoods like Silwan and Sheikh Jarrah.)

The Jewish communities here are a far cry from the hilltop outposts that start with trailers in the rugged reaches of the West Bank. French Hill is filled with professors from the nearby Hebrew University, whose stunning views now include the barrier that separates Palestinian territory from Israel. Ramot has luxurious homes with in-ground swimming pools. Pisgat Zeev has a mall of Israel’s leading chains, while Har Homa, a working-class stretch of apartment blocks whose construction in the 1990s prompted an international outcry, is studded with state-of-the-art playgrounds.

Jerusalem’s mayor, Nir Barkat, has embarked on an ambitious development plan since his election in 2008. The city’s maps do not mark neighborhoods as Jewish or Palestinian, and Mr. Barkat’s aides say the new construction is meant to benefit both communities.

“Jerusalem must remain a united city under all circumstances,” Mr. Barkat said in an e-mail interview this spring about the Givat Hamatos development. “There is no example of a split city, divided either administratively or geographically, that ever worked. Ask Berliners what they think of the idea.”

But Hanan Ashrawi, a member of the Palestine Liberation Organization’s executive committee, said Israel is moving at “a mad pace” to “impose its own solution” to the conflict.

“They want to predetermine the fate and status of Jerusalem,” she said in an interview on Saturday. Israel, she said, “does everything to create on the ground facts that would make any solution impossible.”

If construction in E1 would be “the fatal heart attack” of the two-state solution, as Mr. Seidemann describes it, Givat Hamatos is its “silent killer, high blood pressure.” With a four-part plan including 4,000 homes and 1,000 hotel rooms, it would be the first new neighborhood built in Jerusalem since Har Homa. Like E1, it too would be a roadblock to plans for a contiguous Palestinian state, splitting Bethlehem and the southern West Bank from the thriving Palestinian neighborhood of Beit Safafa and the rest of Jerusalem. “It will kill the village,” said Mahmoud Zohar, 46, who lives in Beit Safafa at the foot of Givat Hamatos. “The village is getting suffocated.”

While the Hamatos plan includes housing for Palestinians, Hagit Ofran of Peace Now’s Settlement Watch Project said a similar provision in Har Homa never came to fruition. Since 1967, she said, Israel has built over 50,000 houses occupied by Jews, and fewer than 700 for Palestinians.

“It’s not only to be able to connect the dots between one Palestinian house and another, it’s also to be able to expand the Palestinian cities,” Ms. Ofran said to explain her objection. “Some people say, O.K., let’s build an underpass or an overpass, but what future will they have?”

A few miles away in E1, there is already such a road, built in 2007, its lanes divided by a concrete wall designed to look like Jerusalem stone. One side is meant for Israelis, and would have exits to Maale Adumim and various parts of Jerusalem. The other, for Palestinians, would have few offramps but provide a path from Ramallah to Bethlehem to answer criticism about contiguity.

The road is fenced off, as is a never-used bridge from E1 to Maale Adumim, since all previous efforts to build in the area have been halted.