The answer to this question will be clear in less time than most of the world would hope. The prelude to most kinds of military action begins with an escallation in rhetoric followed by efforts to rally world opinion and finally by seeking excuses to provoke and antagonise by any means necessary.
The rhetoric is increasing rapidly on both sides where the USA is rattling the sabre on excuses of nuclear weapons as well as accusations of Iranian support of the Iraq insurgency. Iran in retaliation is becoming increasingly belligerent and is also beginning to seek out allies in an all out attempt to spread as much fear and doubt around the world. There are plenty of disaffected countries and kindred islamic regimes that are so anti-American that it is not difficult for Iran to retain the world spotlight as many of the more extreme and militant countries align against the West. Iran will gain allies without much effort and this strikes fear into most Western nations. The USA cannot affort to permit a cohesive allience threaten it's military dominance of the Middle East and will do anything necessary to prevent this from happening.
The USA in turn is working furiously to rally world opinion in it's favour and shore up existing allies. It is also irrevocably committed to proving conclusively that Iran is actively supporting insurgents in Iraq by supplying arms, training and safe passage into the country. This is a desperate ploy that, if unsuccessful, will prove disasterous and cause a loss of face beyond recovery.
The provocation began when the USA captured alleged Iranian nationals in Iraq. The captives stand accused of supplying arms, money and training for insurgents claims the Iranians are strenuously denying. To complicate matters further, Iran counter claims that captives are in fact diplomats. The fire gets hotter!
The final stages are preparation of the American people and the world in general by talk of military strikes. This is a very carefully managed campaign of denials, non-denials, all of which leave little doubt that something serious is imminent. There is also enough room to back out at the last minute without serious loss of face if for some reason the USA assess the risk as too great however should the attack proceed, nobody will be the least bit surprised.
While military action is not a certainty, it is more likely than not given the propensity of the USA to attack and ask questions later. I believe it is a matter of time before the USA strike and the consequences are likely to be quite disastrous everywhere in the world.