With mass protests erupting throughout Egypt calling for the resignation of longtime President Hosni Mubarak, Israel is starting to fret about security implications vis-a-vis the Palestinian Territories and, most importantly, the Gaza Strip.

The Associated Press reports that:

Israel watched fearfully Saturday as anti-government unrest roiled Egypt, one of its most important allies and a bridge to the wider Arab world...

If Egypt's Muslim Brotherhood -- the main opposition group -- gains power in the turmoil, the balance of power between the rival Palestinian camps could change. Abbas is backed by the West, while his Islamic militant Hamas rivals draw their support from Iran, Syria and Hezbollah. Hamas is the Gaza branch of the Muslim Brotherhood.

In the Israeli press, liberal daily newspaper Ha'aretz ran a story headlined "Without Egypt, Israel will be left with no friends in Mideast" that noted:

The friendship between Mubarak and Netanyahu is based on a mutual fear over Iran's strengthening and the rising power of Islamists, as well as over the weakening and distancing of the U.S. government with Barack Obama at its head.

Now, with Mubarak struggling over the survival of his government, Israel is left with two strategic allies in the region: Jordan and the Palestinian Authority. These two allies promise to strengthen Israel's Eastern battlefront and are also working to stop terror attacks and slow down Hamas.

But Israel's relationship with these two allies is complicated. Joint security exercises are modest and the relationship between the leaders is poor. Jordan's King Abdullah refuses to meet Netanyahu, and Palestinian President Mahmoud Abbas is waging a diplomatic struggle against Israel's right-wing government. It's hard to tell how Jordan and the PA could fill the role that Egypt has played for Israel.

Leaders from both the Palestinian Authority and the Libyan government -- Egypt's neighbors -- called embattled Egyptian President Mubarak on Saturday to express their support.

The Elecronic Intifada noted that:

If the Mubarak regime falls, and is replaced by one less tied to Israel and the United States, Israel will be a big loser...

If the Mubarak regime goes, the United States will lose enormous leverage over the situation in Palestine, and Abbas' PA will lose one of its main allies against Hamas.

With the Hamas-controlled Gaza Strip wedged between Israel and Egypt, with both sides sharing control of border access that is instrumental in maintaining the current blockade against Gaza, regime change in Egypt could entail serious security and political upheavals for Israel.  For the Gaza Strip, such change could mean an end to the embargo and closer relations with Egypt.

It remains to be seen what will transpire, but Palestinian and Israeli observers are closely watching what goes down in Egypt.

Reach Reporter Mary Slosson here.  Follow her on Twitter @maryslosson.