Let's break this down: first, we're not participating (i.e. not dropping bombs on Iran. IOW, we're out. Second, we look the other way when 100-200 Israel planes cross over Iraq, drop bombs and come screaming back the other way (followed by Iranians), and then shoot down whatever surviving Iranian planes are following the Israelis and missiles headed to Tel Aviv, Haifa, etc. IOW, we're in.
Either we're in or we're out. We simply cannot have plausible deniability here - we can't play stupid and say, "Gee, sorry, all of our radar operators must've been asleep or drunk, and we didn't see the Israelis coming or going...but we did see Iran try to attack Israel, so we shot down its planes. Sorry, but we'll try to make sure that this doesn't happen again." It just doesn't work. Either we block Israel from doing this (which I think would be the height of both foolishness AND immorality), or we go in whole hog by sending in about 1,000 cruise missiles and a few hundred fighter-bombers and bombers of our own to make sure the Iranians are smashed but good (IOW beyond any capacity for serious retailiation against anyone). Any option in between guarantees both an insufficient pummelling of Iran AND an Iran pissed off at us and capable of retaliating.
Do we have the cajones or not?