state's security and existence, in a lavish welcoming ceremony at Tel Aviv's Ben Gurion airport at the start of a three-day visit to Israel and the Palestinian territories.
"Our alliance is eternal, it is for ever," Obama declared on a bright morning after Air Force One rolled to a stop, warning that tumultuous change sweeping the Middle East brought both promise and peril for Israel.
"It is in our fundamental national security interests to stand with Israel. It makes us both stronger," Obama said, launching a visit draped in symbolism but bringing little hope of progress towards Israeli-Palestinian peace.
Israeli President Shimon Peres praised Obama as a "remarkable world leader" who had shown a deep personal commitment to protect Israel, taking implicit aim at a perception the US president is not sufficiently warm to the Jewish state.
"A world without your friendship would invite aggression against Israel... In times of peace, in times of war, your support for Israel is unshakeable," Peres said.
Prime Minister Benjamin Netanyahu, with whom Obama has had a prickly relationship, was also effusive.
"Thank you, Mr President, for upholding the Jewish people's right for a Jewish state in our homeland and for boldly defending that right in the United Nations," Netanyahu said.
Obama, Netanyahu and Peres, each wearing a white shirt and a blue tie -- the colours of the Israeli flag -- smiled and joked as they greeted dignitaries.
The US leader then came face-to-face with Israel's preoccupation with security, visiting a mobile battery of the US-funded Iron Dome missile defence system trucked to the airport.
For all the soaring rhetoric, Obama's long-awaited visit -- the debut overseas trip of his second term -- may be marked more by symbolism than serious diplomatic substance and will expose diminished US ambitions of forging peace between Israel and the Palestinians.
The president says he is carrying no new peace plans and instead intends to listen to the new Israeli government and Palestinians disaffected with his approach, leading some experts to question why he is coming at all.
He must also navigate the treacherous regional politics of the Middle East, facing new scrutiny over his wariness of deeper US involvement in Syria as government forces and rebels accuse one another of using chemical arms.
During his visit, Obama will pointedly court the historic symbolism of the Jewish State when he inspects the Dead Sea Scrolls and visits the tomb of Theodor Herzl, founder of modern Zionism.
The choreography is intended to show Israelis, Arabs and political foes back home that Obama is deeply committed to Israel's security and future, despite some scepticism about his motives.
He is on tricky political ground: a survey by the independent Israel Democracy Institute showed that while 51 percent of the Jewish Israeli considered Obama neutral toward Israel, 53.5 percent did not trust him with Israel's vital interests.
So, mounting a charm offensive, Obama will deliver a speech to hundreds of young Israelis on Thursday.
Obama and Netanyahu will have to smooth over an often difficult personal chemistry following previous spats, but the visit is unlikely to narrow differences over how soon Iran will have a nuclear weapons capability.
Obama told Israeli television that Iran would not be able to build a nuclear weapon for "over a year or so."
Netanyahu warned last year that Iran would have the capacity to produce a bomb much earlier, within months from the current date, and questions whether sanctions will change Tehran's calculations.
While he will not bring a specific Middle East peace proposal, officials insist Obama's commitment to a two-state solution for Israel and the Palestinians is undimmed.
Columnist Alex Fishman of Israel's Yediot Aharonot newspaper on Wednesday said that Washington, pushed by new Secretary of State John Kerry, would revive the Arab peace plan of 2002.
Palestinian president Mahmud Abbas hopes Obama will help broker the release of more than 1,000 Palestinian prisoners from Israeli jails and wants $700 million in blocked US aid freed up.
Obama will tell the Palestinians that initiatives like seeking statehood recognition at the UN are counterproductive, while warning Israel that settlement building undercuts the chances of resuming peace talks.
In Israel and Jordan, Obama will experience oases of relative calm in a region rocked by unrest spawned by the Arab Spring uprisings.
But his policy towards Syria's bloody unrest will come under new scrutiny, following new allegations from both government forces and rebels that the other side has deployed chemical weapons.