USA cannot remain neutral if Israel attacks Iran or vice-versa. Remaining neutral in fact will amount to supporting Iran. Of course going with Israel will have its consequences. It will mean going into yet another long and protracted battle, which the US economy can ill-afford at present, but siding with Iran (remaining neutral) is not going to please Iran and its operational arms like Hezbollah. Should USA remain neutral in this war, this will embolden Iran Hezbollah and other Al Qaida and non-Al qaida terrorist organizations to take up a more aggressive stance on islamization of USA, which is their ultimate goal. With Israel gone, USA will have to face full fury of these organizations with some of them in possession of nuclear weapons. In that case too, USA will have to fight a long and protracted battle to save its own country. Should USA take a short term view, it will go with Iran, but should it view the situation in a longer term, going into a short and swift war and finishing Iran's menace once for all will be a cheaper alternative. I am sure the USA like every other country will take the short term view.
Italian FM arrives in Iran to promote economic, political ties (Reuters)
from the article: Netanyahu will ask Obama to threaten Iran strike