(Carolyn Kaster/AP Photo)

ABC News' Jake Tapper and Matthew Larotonda report:

Speaking before the annual conference of the influential American Israel Public Affairs Committee today, President Obama rebuffed calls from the Israeli government and its supporters to more starkly warn Iran against building a nuclear weapon, instead urging Israel's leaders and supporters to allow time for diplomatic pressures to work.

The president also assailed "loose talk of war," which he said only helped Iran.

"I firmly believe that an opportunity remains for diplomacy - backed by pressure - to succeed," the president said, adding that "the international community has a responsibility to use the time and space that exists."

Detailing the various ways the sanctions programs have been effective in squeezing the Iranian regime, the president insisted that "the only way to truly solve this problem is for the Iranian government to make a decision to forsake nuclear weapons. That's what history tells us."

The president asked the audience to "remember the weightiness of these issues; the stakes involved for Israel, for America, and for the world. Already, there is too much loose talk of war," which he said only helped the Iranian government by driving up petroleum prices.

"Now is not the time for bluster," he said. "Now is the time to heed that timeless advice from Teddy Roosevelt: Speak softly, but carry a big stick."

In a message more tailored for his domestic audience than the leaders of Israel sitting before him - especially Israeli Prime Minister Benjamin Netahyahu and Defense Minister Ehud Barak - the man who won the presidency promising to end the war in Iraq noted his "deeply-held preference for peace over war."

Referring to wounded U.S. troops back from Iraq and Afghanistan, he said it was "part of my solemn obligation to the American people, I only use force when the time and circumstances demand it."

The relationship between Obama and Netanyahu, of the conservative Likud party, has become an issue in this heated U.S. election year, with Republicans seeking to paint the president as insufficiently supportive of the Jewish state for pressuring the Netanyahu government to stop building settlements in disputed areas of Israel, and for not being stark enough in his warnings and policy against Iran.

Reports out of the Israeli media leading up to today's meeting at the White House between the president and Netanyahu suggested that the Israeli leader wants Obama to more starkly and directly warn Iran's leaders that if they cross a line in their nuclear weapons program, the United States will take military action.

After asking for breathing room, the president made remarks more along the lines of what Netanyahu may have hoped, noting that "Iran's leaders should have no doubt about the resolve of the United States. … I have said that when it comes to preventing Iran from obtaining a nuclear weapon, I will take no options off the table, and I mean what I say."

That includes all ways American power could be leveraged, he said: political, diplomatic, and economic efforts, "and, yes, a military effort to be prepared for any contingency."

Speaking to a more international audience, the president said: "Iran's leaders should know that I do not have a policy of containment; I have a policy to prevent Iran from obtaining a nuclear weapon."

The president pledged that he would "not hesitate to use force when it is necessary to defend the United States and its interests."

The president today did not diminish the threat from Iran, in contrast to arguments made by some in his own party. He said a nuclear-armed Iran is "counter to the national security interests of the United States. Indeed, the entire world has an interest in preventing Iran from acquiring a nuclear weapon."

He raised the specter of an Iranian nuclear weapon falling "into the hands of a terrorist organization" and almost certainly "triggering an arms race in one of the most volatile regions in the world."

Obama condemned the Iranian government for denying the Holocaust, threatening to wipe Israel off the map, and sponsoring terrorist groups committed to Israel's destruction. (Some have quibbled with the translation that Iranian president Mahmoud Ahmadinejad in 2005 said Irael would be "wiped off the map," arguing that Ahmadinejad actually said the Israeli "regime" must be "eliminated from the pages of history.")

The president also offered a robust defense of his support for the Jewish state.

"When the chips are down, I have Israel's back," he said.

The president noted that during this political season opponents are already raising questions regarding his administration's support for Israel.

"Remember that it's not backed up by the facts," he said after proceeding through a list of times the United States has stood with Israel's government by challenging the Goldstone report, boycotting the commemoration of the Durban conference, supporting Israel after the flotilla incident, rejecting the assertion that Zionism is racism, helping to rescue Israeli diplomats in harm's way during the Arab Spring, and so on.

He also attempted to defend himself against charges that he has not been strong enough against Iran, arguing that the policies of the administration of President George W. Bush were a disaster. When he took office, Obama said today, "efforts to apply pressure on Iran were in tatters. Iran had gone from zero centrifuges spinning to thousands, without facing broad pushback from the world."

Iran was then united and the international community divided. Since then, the reverse is true, and he has led the most aggressive sanctions effort in history against Tehran, he said.

Addressing those who have taken issue with his pressure on Israel's government to take steps to return to peace talks with the Palestinians, the president said he made "no apologies for pursuing peace."

Obama also lauded Israeli Prime Minister Shimon Peres - a far more supportive, and less powerful, member of the Israel government - and said that later this spring he would invite Peres to the White House to present him with America's highest civilian honor, the presidential Medal of Freedom.