The new border fence, such as this section north of the resort town of Eilat, is the most tangible sign of Israel’s growing unease about the upheaval in Egypt. (Joel Greenberg/The Washington Post)

A short drive north from this Red Sea resort town, a new reality is taking shape along Israel’s desert border with Egypt. A lonely frontier road flanked by a low, rusting fence is buzzing with earth-moving equipment and workmen erecting an imposing steel barrier encased in razor wire that is gradually snaking across the desolate landscape.

The new border fence, about 15 feet high, is the most tangible sign of Israel’s growing unease about the upheaval in Egypt, which has aggravated shaky security conditions in the Sinai Peninsula bordering Israel. Israeli concerns were heightened in August when gunmen who crossed from Sinai struck on the border road north of Eilat, leaving eight Israelis dead.

That attack led to the acceleration of work on the border fence, which, when complete, will run about 140 miles from Israel’s border with the Gaza Strip south to the Eilat area. Originally intended as an obstacle to the thousands of African migrants and asylum seekers who sneak across the frontier annually, the barrier is increasingly seen as a bulwark against security threats emanating from Sinai.

But the rising fence is also a metaphor for how Israel sees itself in a changing Middle East: Beset on all sides by profound shifts in its Arab neighbors that could alter the strategic balance in the region, it is bolstering its defenses and preparing for the worst.

Lawlessness in the Sinai Peninsula, where local Bedouin tribes have long complained of neglect by the Egyptian authorities, has increased since Egypt’s revolution early this year. Attackers have targeted police posts and repeatedly blown up a natural gas pipeline supplying Israel, leading the government to dispatch additional security forces to the region.

Israeli officials say members of radical Islamic groups and Palestinian militants from the Gaza Strip are seeking to use Sinai as a platform for attacks on Israel. Some have cautioned that the political turmoil in Egypt, and the possible emergence of a government with a strong Islamist element, could threaten the 1979 Israeli-Egyptian peace treaty. The pact has kept the border calm and is seen as a key element of Israel’s security.

Matan Vilnai, the Israeli minister for civil defense and a retired general, said in an interview with Israeli Army Radio last week that he expected a “serious erosion” of the peace treaty with Egypt when its new political leadership emerges. But Prime Minister Benjamin Netanyahu has been more circumspect, declaring that preserving the treaty remains an interest of both Israel and Egypt, regardless of what government emerges there.

For now, the border remains relatively quiet but potentially volatile. Bedouin smugglers and illegal migrants continue to cross the still-porous frontier, and beefed-up Israeli forces are on alert for infiltration by gunmen seeking to attack inside Israel. The smugglers move arms, drugs and other contraband, while the migrants from countries such as Eritrea and Sudan make the risky crossing to seek a livelihood and asylum in Israel.

On Nov. 23, two Egyptian border guards were killed in a shootout with smugglers, according to the Israeli army and news media reports from Egypt. About an hour later, Israeli soldiers shot at a group of smugglers who had crossed into Israel, drawing return fire from the infiltrators, who left behind an assault rifle and a pistol, according to the military.

Events at the border can have a powerful ripple effect. After the deadly attack in August, Israeli forces pursuing the gunmen killed five Egyptian security officers, triggering a furious reaction in Egypt that shook bilateral relations and fueled protests that climaxed three weeks later with the storming of the Israeli Embassy in Cairo.

The area where the attack occurred was eerily quiet during an army-escorted visit by journalists on a recent afternoon. The Israeli border road, closed to civilian traffic since the incident, was empty. Across the new border fence, a group of off-duty Egyptian policemen trooped out of their hilltop post for an impromptu soccer game in the gully below.

Swathed in coils of razor wire, the barrier was angled at its top toward Egyptian territory to discourage attempts to scale it. Sections of the old ramshackle fence were visible in the rocky terrain, separated by gaps that have made it easily passable.

An Israeli surveillance blimp floated in the distance, a sign of the stepped-up intelligence-gathering effort in the border area, coupled with a substantial increase and upgrade of troops at the frontier. The new fence is to be backed by cameras and radar to detect movements on the Egyptian side.

Built to serve as a formidable obstacle rather than as an electronic tripwire to signal infiltration, the Egypt border fence is a larger construction than Israel’s security fence around the Gaza Strip. Located in a barren strip of land along a mutually agreed border, it has not generated the controversies and legal challenges triggered by Israel’s separation barrier in the West Bank, which slices into the territory, runs through Palestinian communities in some places and cuts villages off from their lands in others.

A senior officer on the border with Egypt said that despite the increase in perceived threats there, the army still views the area differently from the hostile frontiers with the Gaza Strip, Syria and Lebanon, from which rockets were fired across Israel’s northern border Tuesday, drawing Israeli artillery fire. The rules of engagement along the Egyptian border were different, the officer said, but he acknowledged that since the August attack, military activity along the borderline is carried out with greater tactical caution and more potential firepower.

“We’re more alert, more prepared, but we still rely on the Egyptians to do the job in their sector,” said the officer, who spoke on the condition of anonymity because of army rules. “We can’t prevent shooting from the other side, but we want to prevent infiltration by terrorists into our territory and attacks inside Israel.”

The $360 million fence project is slated for completion toward the end of next year, and there are plans to reopen the border area soon to Israeli motorists and hikers. Despite the changes sweeping Egypt, coordination with the Egyptian security forces in the field is continuing, the officer said.

“It’s still a border of peace,” he said. “Our interest is to keep it that way.”