The fact that Egyptian attack helicopters are patrolling the Sinai’s lonely skies for the first time since 1973 — striking at bands of Islamist fighters in the Suwarka Bedouin lands in and around el-Arish, some 20 kilometers from Israel’s border — is the lesser of two evils, at least as the IDF sees it.

For the defense establishment, the 60,000-square-kilometer Sinai desert is “a screen of sand,” a strategic buffer zone that, so long as it remains relatively demilitarized, guarantees against a surprise attack.

Today, however, military officials believe that Sinai’s festering terror cells pose a greater threat to peace than the bending of the Camp David Accords.

Defense Minister Ehud Barak said Monday he hoped the Sunday attack, which saw 16 Egyptian border police killed before the terrorists were thwarted upon trying to infiltrate Israel, would constitute a wake-up call for Cairo. If the alarm is now being heeded, Jerusalem is not about to complain.

In any case, some say, Egypt is too burdened by domestic troubles at this point to even think about attacking Israel.

It was not always this way.

Israel in the past saw the precise demilitarization of the Sinai as specified in the 1978 Camp David Accords as critical.

The peace agreement split the peninsula into four north-south zones. The first, A, runs north from Sharm el-Sheikh to St. Catherine to Bir al-Abd on the Mediterranean. Only within that region are the Egyptian armed forces allowed to keep one mechanized or armored military division. The other three zones are restricted to police units with light weapons.

Opinions have varied as to whether the current Egyptian action is a violation of that agreement –- and thus a potential precedent for wider, and potentially incendiary violations.

But the fact is, in recent years, Jerusalem has been quietly pulling back from some of the agreement’s most rigorous limitations.

According to Ehud Yaari, an Arab affairs analyst for Channel 2, Israel and Egypt, under the auspices of the peacekeeping Multinational Force and Observers, reached an unpublicized agreement 10 years ago allowing Cairo wider latitude in the Sinai. The Agreed Activities Mechanism, he wrote in a paper on Islamist extremism in the Sinai for the Washington Institute for Near East Policy, allows Egyptian military forces to operate east of Zone A, in Zones B and C, and has been implemented both before and since the 2011 revolution in Egypt.

In the long-term, the defense establishment believes that Israel’s historic peace ties with Egypt will come under increasing strain, now that Hosni Mubarak has gone and the Muslim Brotherhood’s Mohammed Morsi is president. “There is an expectation for a deep change in Egypt’s ties with Israel over the [coming] years,” Maj. Gen. Aviv Kochavi, the head of the IDF Intelligence Corps, told a Knesset committee two weeks ago.

And that was before the band of Sinai gunmen killed 16 Egyptian border policemen and attempted to infiltrate Israel on Sunday night. Their action in turn led to Wednesday’s response, as Egypt rolled in tanks and took to the skies in a bid to clear the peninsula of terrorists. But it could have also led to armed hostilities between Israel and Egypt.

Senior IDF spokesperson Lt. Col. Avital Leibovich, said that the brazen Sunday evening attack, which included several terrorists armed with suicide belts and a truck carrying 1,000 pounds of explosives, was “certainly meant to kill as many Israelis as possible” — and to destabilize the fragile Jerusalem-Cairo relationship.

The attack on the Egyptian personnel in the initial stage of the attack, which she characterized as “sophisticated,” was merely “a stop on the way” to Israel, she said.

Brig. Gen. (res) Shalom Harari, a former adviser to the defense ministry, said he had “no doubt that the rationale for the attack was to cause conflict between Israel and Egypt.”

Terror bands along Israel’s borders have managed to draw the army into conflict in the past.

From 1950-1970, Palestinian Fedayoun and Palestine Liberation Organization terrorists crossed into Israel from Jordan, which led to armed clashes between the IDF and the Jordanian army. In September 1970, after the Palestinian terror turned against the Hashemite Kingdom, King Hussein launched a military operation, killing thousands of Palestinians and ousting the PLO from Jordan.

In the south of Lebanon they set up camp again, in an area known as Fatahland, and the murderous cross-border raids of the seventies and the constant rocket fire from the north sparked Israel’s invasion of Lebanon in the summer of 1982.

Egypt seems to represent the latest iteration of this series. Last August, a terrorist infiltration across the border north of Eilat left eight Israelis dead, and caused a reported three fatalities among Egyptian forces — an incident which in turn led to anti-Israel protests in Cairo and the storming of the Israeli Embassy, in which only an eleventh-hour rescue prevented Israeli loss of life.

So far, relatively cool heads have prevented a drastic deterioration in ties between Cairo and Jerusalem. But incidents such as those last August and on Sunday can easily send the situation spiraling out of control.

As it braced for Sunday’s attack — issuing terror warnings based on intelligence information, and trying to alert Egypt to the looming danger — the IDF remained in strictly defensive mode, waiting for the terrorists to come Israel’s way. That defensive posture is clear, too, in the accelerated work on an effective border security fence.

But if the sophisticated Sinai terror cells can survive the current Egyptian air and ground assault and continue to cause casualties along the border, or if they prove capable of mounting a large-scale attack — such as the downing of a plane, or the sinking of a ship near Eilat, which Hebrew media this week described as a realistic concern — then, according to senior research analyst for the Jerusalem Center for Public Affairs Dr. Jacques Neriah, that could “put an end to Israeli restraint.”