Even the more routine assistance under discussion — including equipment and training of its border police — has faced resistance, but after talks last week, the officials said they were optimistic that Mr. Morsi’s government would allow greater military-to-military collaboration.

While concerns about security in Sinai have intensified during the tumult of the Arab Spring, they are not new. Nor are American offers of military assistance to deal with a problem with multiple causes, including terrain, the government’s neglect of the Bedouin tribes that roam through the sparsely populated area and the treaty with Israel limiting military personnel and firepower.

Militants — some linked to international terrorist organizations, some to the Palestinian territories and some homegrown — have mounted large attacks before, including coordinated bombings in 2005 that killed nearly 100 people in Sharm el Sheik, the Red Sea resort favored by Mr. Mubarak and foreign tourists.

In 2007, after a series of rocket attacks from Gaza into Israel, Mr. Mubarak’s government — including the current military leader, Field Marshal Mohamed Hussein Tantawi — relented to pressure by then Secretary of State Condoleezza Rice and allowed the United States Army Corps of Engineers to draw up plans for improving security on the border, according to diplomatic cables disclosed by WikiLeaks.

That work led to a $23 million project to deploy seismic sensors to detect tunnels used by smugglers hauling contraband and weapons between Gaza and Egypt, though that was undermined in 2009 when Field Marshal Tantawi refused to allow a satellite link to the sensors that would record GPS coordinates. Reflecting the sensitivity to matters of sovereignty, he cited “potential criticism from the opposition of U.S. control over the Egyptian border.”

Mrs. Clinton and Mr. Panetta both raised alarms about security in Sinai in their recent meetings with Mr. Morsi and Field Marshal Tantawi — in Mr. Panetta’s case just days before the attack.

“We indicated concerns about some of the security threats there, some of it the result of border efforts that have not been sometimes effective at controlling individuals and weapons that have come through,” Mr. Panetta said after the talks with Mr. Morsi in Cairo last month.