I’d be skeptical about the report, not so much about whether such a plan exists (it might), but about how serious the plan is. The Israelis likely have dozens of different scenarios drawn up for a possible military strike on Iran, and this was likely just a plan rather than the plan. Israel also may have leaked this as their way of responding to Iran’s “wipe Israel off the map” rhetoric by putting them on notice that Israel is prepared to use tactical nukes preemtively. Also, another factor is that Israel may have leaked it to pressure the U.S. and international community into taking a harder line against Iran. One of the things that motivated Nixon to airlift aid to Israel during the Yom Kippur War in 1973 was the fear that a desperate Israel, caught by surprise and fighting for survival on its heels, would use a nuclear bomb on Damascus. Perhaps the U.S. and Israel can play good cop/bad cop, with the U.S. arguing that if the international community doesn’t take harsher measures against Iran, Israel may use tactical nukes, which would inflame the entire Arab and Muslim world.
With all that said, even though, as has been pointed out by John and in comments, the U.S. is better equiped for a quick strike against Iran, Israel may end up doing it because it has the most to lose from a nuclear Iran. While an Iran with nuclear weapons would be a threat to the U.S. and other countries, it would be a clear existential threat to Israel. After our adventure in Iraq, public opinion in the U.S. would be divided if not overwhelming againtst a preemtive strike on Iran, whereas Israelis would support one. These realities will likely cause the U.S. to hesitate and debate a military strike longer, which makes it more likely that Israel will strike first.