As Ehud Olmert visits US President George W. Bush, headlines around the world focus on coordination in US and Israeli policies towards new realities in Gaza. However, the significance of recent events in Gaza should not overshadow discussion of essential differences between the two allies regarding issues of Israeli national security - specifically the Iranian nuclear project. Although the US and Israel share a larger goal of preventing Iran from obtaining nuclear weapons, each party has different regional priorities, faces different policy constraints and has different stakes. While Israel perceives a nuclear-armed Iran as its most serious existential threat, the US foreign policy agenda is littered with other pressing problems. America's number-one priority is the stability of Iraq and the withdrawal of US forces. Any US policy decision vis- -vis Iran will be colored by how best to satisfy America's interests in Iraq. In fact, debate in the US is still ongoing over which is preferable - seeking to contain a nuclear-armed Iran or preventing Iran from even acquiring the technology to build a bomb. In the minds of most Israeli decision-makers, for whom the stakes of a nuclear Iran are clearly much higher, there is no debate on which path is acceptable. In addition, the US is constrained in its possible actions towards Iran, both regionally and domestically. Iran possesses direct influence over Iraq's stability through its patronage of Iraqi Shi'a parties. Iran has other leverages over the US, revealed in recent allegations that it supports the Taliban insurgency in Afghanistan and would attack US interests in the Persian Gulf should Washington consider military action against Teheran. Moreover, the Bush administration faces domestic constraints. The war in Iraq eroded American public support for unilateral military action and Bush is under tremendous pressure both inside and outside his administration to be far more multilateral and diplomatic concerning the Middle East. Although Bush rejected the Baker-Hamilton recommendations, his administration has in practice adopted its call for a regional, diplomatic approach, as evidenced by the recent landmark meetings between US and Iranian officials concerning Iraq. What does the US trend towards multilateral diplomacy in the region mean for Israel's freedom to act - even unilaterally or militarily if necessary? A scenario in which the US and Iran negotiate, directly or indirectly, would likely involve US pressure on Israel to show restraint. Similarly, in the event of direct US-Iran talks, US coordination with Israel - which refuses to accept a nuclear Iran and sees the Islamic regime's fingerprints on Syria, Hizbullah and Hamas actions - could be a burden for US ability to get the outcomes it needs in Iraq. Israel has been in favor of an international solution to the global Iranian challenge, but if that international solution involves some kind of American-Iranian deal, Israel's challenge will be to ensure that any incongruence with the US does not leave Israel's key national security objectives unfulfilled, its freedom to act constrained and its relationship with the US tarnished. While Hamas and Fatah dominate the agenda of the Bush-Olmert talks, Israel should clarify outstanding differences between Israel and the US concerning Iran. Despite areas of incongruence between Israel and the US, Israel must obtain guarantees from its indispensable ally that when the moment of Iranian-US reckoning arrives, Israel's essential national security interests will not be forgotten. The writer is an analyst at the Reut Institute.