Rafah, Gaza Strip ? The collapse of Egypt’s border with the Gaza Strip on Wednesday altered the region’s political and security landscape as suddenly as it changed the lives of Palestinians who poured out of the enclave to stock up on goods made scarce by an Israeli blockade.

After masked gunmen used land mines to blast through a seven-mile-long border wall, tens of thousands of jubilant Gazans went on an Egyptian buying spree for gasoline, heating oil, rice, sugar, milk, cheese, cigarettes, tires, cement, television sets and mobile phones.

But the breach stirred alarm in Israel over the prospect that Palestinian militants could return with weapons, slipping into crowds of shoppers lugging household merchandise to the impoverished territory run by the Islamic movement Hamas.

Israeli leaders were stunned by the sudden turn of events, which gave Hamas at least a temporary victory over their effort, backed by the United States and Egypt, to keep Gaza isolated. Hamas planned or at least tolerated the barrier’s demolition, and its policemen directed the cross-border traffic.

The endeavor to contain and weaken Hamas is a cornerstone of President Bush’s strategy for brokering a peace accord between Israel and the secular-led Palestinian Authority, which continues to control the West Bank. Hamas, which advocates Israel’s destruction, has allowed Gaza to be used for near-daily rocket attacks against Israel that threaten to undermine the peace talks.

Now the United States and Israel, which have been pressing Egypt to halt weapons smuggling to Gaza, face unsettling new scenarios: a freer flow of weapons across a chaotic, open border; rising Islamic, pro-Palestinian militancy in secular-led Egypt; and a loosening of Gaza’s long-term border control arrangements.

“Our concern is not that anyone is going to Egypt to buy food,” said Arye Mekel, an Israeli Foreign Ministry spokesman. “Our concern is that when Gaza’s exits are open, the entrances are open too, for more weapons, explosives and missiles. For us, that could make a bad situation in Gaza a lot worse.”

“We expect the Egyptians to solve the problem,” he said.

The open border also poses a risk for Egypt: weapons smuggling in the opposite direction, from Gaza to anti-government militants in Egypt’s Sinai region.

Egyptian President Hosni Mubarak’s government has been under fire from Islamists at home for not doing enough to help the Palestinians. On Wednesday, riot police in Cairo dispersed 2,000 people led by the outlawed Muslim Brotherhood who tried to hold a rally to protest the Israeli blockade. Egypt’s Foreign Ministry and Hamas’ leadership used Wednesday’s chaos to call for international talks on revising the protocol for controlling Gaza’s borders and steps to ease the territory’s isolation.

Many of Gaza’s 1.5 million residents have suffered shortages of electricity, fuel, medicine and other supplies for months. Gaza has been all but sealed since Hamas seized control of the territory and its border crossings from Palestinian Authority President Mahmoud Abbas’ secular Fatah faction last June.

Israel had further tightened the sanctions last week, cutting off fuel for Gaza’s only power plant in response to a sharp increase in rocket attacks on targets across the border in Israel. The blockade was eased only slightly on Tuesday.