Why tell US and not do it on their own? Israel with one of the world's best Air Force, and it should be a piece of cake to do it on their own even without the help of US. America won't intervene, and will wave hands as they pass over Iraq.
Just guessing, of course, but I think the taking out of the nukes would present an opportunity for getting rid of the entire hardline government. And as long as Ahmadinejad and the Ayatollahs are in power, they are going to threaten Iraq. In fact, when we leave Iraq, I think they will slide in (unless they are gone).