Israel can't openly discuss the idea of arms reduction or sign any official treaties on the issue otherwise it would mean an end to the ambiguity policy and neither Israel, the US, Russia or even the arabs want that to change. The ambiguity policy suits everybody arabs especially because if Israel doesn't actually have nukes the arab governments who don't want to invest in a nuclear weapons program don't need to develop them. If Israel did have nukes then they would have to think twice. Its all a big diplomatic game which everybody benefits from.
from the article: Israel's atomic arsenal could fall victim to a new U.S. nuclear policy