The bad news is that most Americans are ill-informed about the Iranian nuclear program; the good news is that they still don't want to attack Iran. Those are results of the biennial Chicago Council on Global Affairs survey of public opinion on foreign policy (PDF).
The bad news first: Who can blame them? There's a constant stream of misinformation out there, and so a stunning majority of 66 percent of Americans don't know that U.S. intelligence agencies think Iran has not made a decision to build a nuclear weapon. Here's the chart from the Chicago Council:
While nearly two-thirds of Americans see Iran as a threat (down a bit from two years ago), slightly more still want their government to talk to the Iranians. What don't Americans want? A war with Iran, especially not a unilateral one (my emphasis):
A slim majority (51%) opposes UN authorization of a military strike against Iran’s nuclear energy facilities, with a substantial minority (45%) supporting such action. A far broader majority (70%) opposes a unilateral strike by the United States if Iran continues to enrich uranium but the Security Council does not authorize a military strike.
That means even some of those Americans who think Iran is hellbent on developing weapons—or that Iran already has them—don't support an attack.
Americans aren't that keen on the idea of an Israeli attack on Iran's nuclear program either: 59 percent of respondents to the Chicago Council said the U.S. shouldn't commit military forces to help Israel in the event that an Israeli initiated-strike touches off a broader conflict. Nearly four-in-ten said the U.S. should jump in.
Instead of an attack, Americans support unilateral and multilateral sanctions (such as pressure from the U.N. Security Council), and direct diplomacy. Whose policy does that sound like?