TEL AVIV—Israel fears that the victory of Islamist Mohammed Morsi in Egypt´s presidential election is likely to erode the already delicate ties between the two countries, testing one of the Middle East´s important strategic links.

Most Israeli officials expect the Muslim Brotherhood leader to uphold a promise to preserve the 33-year-old peace treaty between Egypt and Israel. But many analysts say they expect the "cold peace" between the countries to get chillier.

Prime Minister Benjamin Netanyahu reiterated Monday that Israel respects the Egyptian vote and said he looks forward to working with the new administration. "I believe that the peace is important to Egypt," he said. "And I believe that the peace is the fundamental pillar of stability in our region." Last year, however, he warned that Egypt´s revolution against longtime President Hosni Mubarak, who often worked in silent partnership with Israel on security, could empower Islamist radicals.

Israeli cabinet ministers and officials were largely silent for fear of upsetting the fragile ties. "The situation in Egypt is too unstable to say anything more," said an Israeli official. "We don´t know anything about what is going on there."

The two countries´ defense establishments enjoy robust working ties. The peace treaty between the sides is linked to $1.3 billion in U.S. military aid to Egypt. But there is concern that Mr. Morsi will adopt a more confrontational public stance toward the Jewish state while strengthening ties with Hamas, a militant offshoot of the Muslim Brotherhood that refuse to recognize Israel or foreswear violence. Hamas runs the Gaza Strip.

There is an expectation among many Israel observers that the new Egyptian president won´t push to reverse growing chaos in the Sinai Desert that has led to cross-border attacks into Israel, including an ambush last week that killed one building contractor. Israel has accused militants from Gaza of using the peninsula as a base for such operations, and has launched retaliatory attacks into the strip.

Israel is also waiting to see the outcome of the power struggle between Mr. Morsi and the generals who have served as Egypt´s interim rulers, with some seeing an echo of the tension in Turkey between Islamist politicians and the army.

"After Morsi´s rise to power, everything is open and unclear," Alex Fishman, a defense commentator, wrote in the daily Yediot Ahronot newspaper. "Egypt has not become this morning an enemy state threatening Israel´s borders, but the intelligence and military establishment in Israel should nonetheless regard the old friend as a country that has to be relearned, and should prepare accordingly."

Israel has already rushed construction over the past year on a fence about 160 miles(250 kilometers) long to seal off the frontier with Egypt, and it has also bulked up its patrols along the border. With Mr. Morsi´s victory, Israel may need to adopt a new policy for using force in the Gaza Strip, experts say, given the new risks of fallout inside Egypt.

"The Muslim Brotherhood in general is committed to honoring Egyptian commitments from international agreements, and they´re likely to do that," said Shimon Shamir, a former Israeli ambassador to Egypt. "The main question is what will happen if a crisis breaks out. In that case, the relations could be affected much more than in the era of Mubarak. It is likely that Egypt, which is ruled by Morsi, will probably react more strongly, and the relations will become more endangered."

Reflecting public anxiety over the Muslim Brotherhood´s ascendence in Egypt, Yediot Ahronot ran a front-page headline "Darkness in Egypt"—a Hebrew pun referring to one of the 10 biblical plagues visited on Egypt prior to the Israelites´ exodus. Israeli news websites featured a report from an Iranian state news agency that Mr. Morsi plans to warm relations with Tehran. Cairo denied the report.

Despite heightened concern about a decline in relations, Israeli military planners haven´t sought billions of dollars to rebuild the conventional Israeli forces that would face Egypt in any war. Such a decision would reflect a strategic shift in Israel´s long-term thinking about relations with its southern neighbor.

The 1979 peace treaty with Egypt gave Israel´s economy a substantial peace dividend in the form of lower defense spending, and served as a precedent for subsequent peace talks with the Palestinians, Jordan and Syria.

A key question facing Israeli policy planners is whether Mr. Morsi will hew to the Muslim Brotherhood ideology that negates Israel´s existence and calls for the establishment of an Islamic caliphate on historic Palestine—or, instead, whether he will seek a way to accommodate Israel and focus domestic concerns like promoting economic growth.

Dore Gold, a former ambassador to the United Nations, said that while the Brotherhood has a "worrisome ideological baggage," Israel will need to monitor the division of power between the military and the civilian government, and the new president´s efforts to revive the domestic economy.

"If the Muslim Brotherhood continues to maintain the kind of jihadist language that is on its website, then the Egyptian economy will go nowhere,´´ he said. "Unfortunately, the past record of Muslim Brotherhood regimes in power in Sudan in the 1990s...and in Gaza under [Hamas leader] Ismail Haniyeh is not a source of encouragement." (Copyright © Dow Jones & Company, Inc.) 06/26/12)