As for a preemptive attack, which I imagine you meant would be nuclear since they're already giving it all they've got with their non-nuclear attacks, it is already clear that Israel and USA don't have a way to stop Iran's faster missiles, and they would have no way to prevent Iran nuking Tel-Aviv and Haifa in return. At that point Israel would cease to exist as a state and as a society. They would never risk that. The entire decades-long war against the middle east by USA and Israel is fought for the benefit of Israel, not for its destruction.
Israel generally has fairly solid intelligence in Iran and would almost certainly take whatever action is necessary to prevent Iran from building a Nuke...potentially all the way up to using small tactical nukes in targeted strikes on nuclear facilities if conventional attacks would be insufficient. Any preemptive attack would likely occur before Iran actually were acquire a viable nuclear weapon.
> Furthermore, if Iran declared that it did possess working nuclear weapons that wouldn't be a deterrent: it would trigger an immediate and massive preemptive attack by the USA and Israel.
I've been discussing this under the assumption from your own words that "it did possess working nuclear weapons" ('it' being Iran). If you are now changing this to a massive escalation before they even get it, then that is out of scope for this discussion. I would argue they are already doing that to the extent that they can, as they have to tread carefully since Iran can also destroy all key infrastructure in Israel as well.
'Working nuclear weapons' is a really broad scale so it's tough to extrapolate without knowing if it means "they can send a person with a low yield weapon somewhere and blow it up vs. "they can launch a high yield weapon on a ballistic missile anywhere within 2000km"