An older article (12 Aug 04) from CNS/MIIS, but still worth the read:

A Preemptive Attack on Iran's Nuclear Facilities: Possible Consequences
At a time when Iraq and the war on terrorism tend to dominate the debate on international affairs, the possibility of an attack on Iran's nuclear facilities has not been a major topic of discussion in the United States. There are reports, however, that the Bush administration has seriously considered this option but opted to put it on the back burner for the time being. Further, on May 6, 2004, the U.S. House of Representatives passed Resolution 398 in a 376-3 vote, calling on the U.S. government "to use all appropriate means to deter, dissuade, and prevent Iran from acquiring nuclear weapons." If a similar resolution passes the Senate, it will give President Bush or any future administration the ability to launch a preemptive strike on Iran's nuclear facilities whenever this is deemed necessary.

In Israel, planning and rhetoric appear to have progressed quite a bit further; it appears that some in Israel are seriously considering a preemptive attack similar to the June 1981 attack on Osirak that destroyed Iraq's nuclear reactor. Meir Dagan, the Chief of Mossad, told parliament members in his inaugural appearance before the Israeli Knesset Foreign Affairs and Defense Committee that Iran was close to the "point of no return" and that the specter of Iranian possession of nuclear weapons was the greatest threat to Israel since its inception. On November 11, 2003, Israeli Foreign Minister Silvan Shalom said that Israel had "no plans to attack nuclear facilities in Iran." Less than two weeks later however, during a visit to the United States, Israel's Defense Minister Shaul Mofaz stated that "under no circumstances would Israel be able to tolerate nuclear weapons in Iranian possession" and just six weeks earlier, Mossad had revealed plans for preemptive attacks by F-16 bombers on Iranian nuclear sites. This report will examine the following: The Iranian nuclear facilities most likely to be targeted and their proliferation risk potential; the likely preemptive scenarios involving Israel or the United States; and the possible consequences of any preemptive action...