If it came to the point that Israel would have to Strike Iran, I beleive the US would allow an Israeli flyover possibly even support it with KC-135's to get them there, If not they would go NOE and do it anyway.Imagine how many American lives would be in danger in Iraq if the Iranians have these weapons.
Also, Underground facilities are no longer free from being targeted, just look what we did in the Gulf War and Enduring Freedom.
The Israelis are there own country, and if there National Security was in danger, by missiles that could lob warheads on them, then they wouldnt care what we said. Off topic but Just look at what was going on in Yom Kippur, We support the Israelis by delivering A-4 Skyhawks, the situation in the Middle East is seconds away from World War 3, with Soviet and American Ships clogging the Med, and the Israeli's are doing Mock attacks on the US battle fleet.
They do what they want, when they want.