The street revolt in Egypt has thrown the Israeli government and military into turmoil, with top officials closeted in round-the-clock strategy sessions aimed at rethinking their most significant regional relationship.
Israel's military planning relies on peace with Egypt; nearly half the natural gas it uses is imported from Egypt; and the principle of trading conquered land for diplomatic ties began with its 1979 peace treaty with Egypt. Prime Minister Benjamin Netanyahu has met with President Hosni Mubarak of Egypt more than with any other foreign leader, except President Obama. If Mr. Mubarak were driven from power, the effect on Israel could be profound.
"For the United States, Egypt is the keystone of its Middle East policy," a senior official said. "For Israel, it's the whole arch."
The official spoke on the condition of anonymity because Mr Netanyahu has ordered his ministers and their officials to stay publicly silent on Egypt while events there play out.
Many analysts here said that even if Mr. Mubarak were forced to leave office, those who replaced him could maintain Egypt's peace treaty with Israel, since it is the basis for more than $1 billion in annual aid to Cairo from Washington and much foreign investment.
But others noted that the best-organized political force in Egypt is the Muslim Brotherhood, which is hostile to Israel and close to Hamas, the Palestinian rulers in Gaza whose weapons-smuggling the Egyptian government works to block.
As the government evacuated the families of envoys from Egypt over the weekend, public affairs broadcasts and newspapers in Israel focused on the unfolding events there. Most of the predictions were dire. Two of three newspapers with the largest circulations, Yediot Aharonot and Maariv, had identical front-page headlines: "A New Middle East."
Despite Mr. Mubarak’s supportive relations with Israel, many Israelis on both the left and right are sympathetic to the Egyptians’ desire to rid themselves of his autocracy and build a democracy.