WASHINGTON – President Obama said Sunday he would not hesitate to attack Iran to keep it from getting a nuclear bomb, hoping a forceful assurance will discourage Israel from launching a unilateral strike that could ignite the Middle East and drag the U.S. into war.

Pleading for time for diplomacy to work, Obama warned that “loose talk of war” was only undermining world security.

Addressing a powerful pro-Israel lobby, Obama delivered messages to multiple political audiences: Israel, Iran, Jewish voters, a restless Congress, a wary international community and three Republican presidential contenders who will speak to the same group Tuesday.

At the core was his bullish assertion that the United States will never settle for containing a nuclear-armed Iran or fail to defend Israel.

“I will not hesitate to use force when it is necessary to defend the United States and its interests,” Obama said.

But he framed military force as a last resort, not the next option at a time when sanctions are squeezing Iran. The president seemed intent on quieting a drumbeat for war, saying even the talk of it has driven up the price of oil to the benefit of Iran.

“Now is not the time for bluster,” Obama said. “Now is the time to let our increased pressure sink in.”

Obama’s speech to the American Israel Public Affairs Committee set a tone for a vital meeting today with Prime Minister Benjamin Netanyahu, whose embattled Mideast nation fears it will soon lose a window to strike Iran before it becomes a target of nuclear weapons.

More than once, Obama threatened force but made clear his preference was peace through pressure.

Netanyahu, standing his ground against what his country perceives as a threat to its existence, said he perhaps most appreciated hearing Obama say “Israel must be able to defend itself, by itself, against any threat.” Speaking to reporters in Canada ahead of his arrival in the U.S., Netanyahu made no reference to the sanctions and diplomacy Obama emphasized.

Iran insists its nuclear program is for peaceful purposes, and escalating sanctions have not deterred its pursuit. It has ramped up production of the higher-grade enriched uranium needed for an atomic bomb.

Obama offered the lines Israel wanted to hear, framing the Iranian threat as a problem for the entire world, and asserting Israel’s right to defend itself how it sees fit.

No assurance was more important than when Obama said he does not have a “policy of containment” toward Iran, but rather one to deny it a nuclear weapon.

Election-year politics, too, were part of Obama’s speech as he spoke of his record on Israel. He told his audience that his Republican rivals would probably distort his record.

“There should not be a shred of doubt by now,” Obama said. “When the chips are down, I have Israel’s back.”

The United States fears an Israeli strike on Iran would do little to derail its long-term nuclear weapons pursuit and, in the near term, would turn Iran into a victim. Many analysts believe an Israeli attack would result in a region-wide conflict, including Iranian attacks on American troops in the Persian Gulf.

Obama is also worried about gas prices, a chief concern to American voters.

“I would ask that we all remember the weightiness of these issues, the stakes involved for Israel, for America, and for the world,” Obama said. “Already, there is too much loose talk of war.”