JERUSALEM -- Calling the U.S. Israel's "greatest friend," President Barack Obama assured the Middle East ally of his administration's commitment to Israel's security while cautioning that the region's "winds of change bring both promise and peril."

Obama declared common cause with Israel, noting that it was the first stop of the first trip of his second term. "We share a vision of Israel at peace with its neighbors," Obama said upon arriving in Tel Aviv.

Israeli President Shimon Peres welcomed Obama, asserting that "A world without America's leadership, without her moral voice, would be a darker world. A world without your friendship, would invite aggression against Israel."

Obama's trip is his first visit to the country - and only his second to the Middle East, outside of a quick jaunt to Iraq - since taking office. He will also be making his first trips as president to the Palestinian Authority and Jordan this week. But on an itinerary laden more with symbolism than substance, an Israel that is increasingly wary of developments in Syria and Iran is Obama's main focus.

Adding yet another dimension to the trip, Obama landed amid new questions about the Syrian regime's possible use of chemical weapons.

Even before leaving Tel Aviv's airport, Obama offered a vivid display of America's commitment to Israeli security by visiting a missile battery that is part of Israel's Iron Dome defense from militant rocket attacks. The United States has invested hundreds of millions of dollars in developing the system with Israel.

Obama and Netanyahu toured the battery on the airport tarmac, meeting and chatting with soldiers who operate the system. The battery is not normally stationed at the airport and was placed there only for the visit. Israel credits Iron Dome with intercepting hundreds of rockets during a round of fighting against Gaza militants last November.

"Thank you for standing by Israel at this time of historic change in the Middle East," Prime Minister Benjamin Netanyahu told Obama. "Thank you for unequivocally affirming Israel's sovereign right to defend itself by itself against any threat."

As he arrived, Obama joked to Netanyahu that he was "getting away from Congress."

Following the arrival ceremony at the airport, Obama headed to Jerusalem for meetings with Israeli leaders.

Obama faces an Israeli leadership and public anxious to hear the president affirm America's commitment to the security of the Jewish state while standing on their soil.

Obama sparred frequently with Netanyahu over the Palestinian peace process during his first term. And despite public assurances from both sides that relations otherwise remained solid, the president endured four years of criticism from pro-Israel advocates and conservatives in the U.S. and numerous commentators in Israel for not doing enough to back the Mideast's only stable democracy in the face of growing threats to its existence.

So even though U.S. officials have set expectations low and previewed no significant policy announcements, there is a clear metric to measure the success of Obama's three-day stay in Israel and the West Bank: how much he is able to reverse the perception that his administration is not fully committed to Israel's security.

The centerpiece of the first leg of the trip will be a speech to Israeli university students on Thursday, during which Obama is expected to renew U.S. assurances to stand by Israel as it seeks to counter threats from Iran and protect its people in the midst of civil war in neighboring Syria, where new questions were raised Tuesday about the Assad regime's possible use of chemical weapons.

Ahead of Obama's visit, an Israeli Cabinet minister, Yuval Steinitz, said it is "apparently clear" that chemical weapons were recently used in Syria, and that the alleged attack will be a main topic of conversation with the president. The Obama administration said Tuesday it had no evidence to support the regime's claims that rebels were responsible for a chemical attack.

Obama has declared the use, deployment or transfer of the weapons would be a "red line" for possible military intervention by the U.S. in the Syrian conflict.

Before he even leaves Ben Gurion airport for the 45-minute helicopter flight to Jerusalem, Obama will stop to view an Iron Dome battery, part of the missile defense system that the United States has poured hundreds of millions dollars into developing. Israeli officials credit Iron Dome with significantly reducing the impact of rockets fired into its territory from militants in the Gaza Strip and Lebanon and don't want to see U.S. funding cut due to budget constraints.

Once in Jerusalem, a potent religious symbol as well as one of the main obstacles to an Israeli-Palestinian peace deal, Obama will make several cultural stops - to see some of the ancient Dead Sea Scrolls and pay tribute to the founder of modern Zionism - intended to show his appreciation for the Jewish people's millennia-old connection to the land that is now Israel as well as the horrors of the Holocaust. He will also visit the Church of Nativity, which is revered throughout Christiandom as the site where Jesus was born.

Obama will make an almost perfunctory visit to the cash-strapped Palestinian Authority's headquarters in the West Bank, where he will meet embattled Palestinian President Mahmoud Abbas to assure him that an independent Palestinian state remains a U.S. foreign policy and national security priority. Despite not coming with any new plan to get the stalled peace process back on track, Obama plans to make clear that his administration intends to keep trying to get talks relaunched.

Preventing Iran from developing a nuclear weapon and the Syrian crisis from spilling over into the broader region are top priorities of Israel and the United States, although they have differed in the past on precisely how to achieve both ends.

Iran, in particular, has been a vexing issue, as Iranian leaders continue to defy pressure from the U.S. and other world powers to prove that its nuclear program is peaceful and not, as many suspect, cover for atomic weapons developments.

Israel repeatedly has threatened to take military action should Iran appear to be on the verge of obtaining a bomb. The U.S. has pushed for more time to allow diplomacy and economic penalties to run their course, though Obama insists military action is an option.

But there are differences over a timeline for possible military action. Netanyahu, in a speech to the United Nations in September, said Iran was about six months away from being able to build a bomb. Obama said last week that the U.S. thinks it would take "over a year or so for Iran to actually develop a nuclear weapon."

Obama will close out his Mideast trip with a 24-hour stop in Jordan, an important U.S. ally, where his focus will be on the violence in Syria. More than 450,000 Syrians have fled to Jordan, crowding refugee camps and overwhelming aid organizations.

In his talks with Jordan's King Abdullah, Obama also will try to shore up the country's fledgling attempts to liberalize its government and stave off an Arab Spring-style movement similar to the ones that have taken down leaders elsewhere in the region.