A report by the Iran Project published in late 2012 warned that "a U.S. and/or Israeli preventive military action against Iran could ... perhaps contribut[e] to increased sectarian conflict and regional war." In March 2012, pundit Fareed Zakaria warned that an Israeli or American strike against Iran could be "a path to another Middle East war." While other experts have actually posited a more measured Iranian response, they have not offered a systematic analysis of Iran's strategic capabilities.
Iran could respond to an attack in two main arenas: against Israel, or in the Persian Gulf against the United States and/or the Sunni Gulf states, mainly Saudi Arabia. The common Western assessment, which envisions a horror scenario of Iranian responses and consequent developments, serves as an excellent deterrence tool for the Iranians by undermining the threat of the military option and reducing the likelihood that the regime in Tehran will agree to a diplomatic solution.
This paper challenges the commonly held Western view through a systematic analysis of Iran's capabilities and the possible range of Iranian strategies to be used against Israel. The analysis complements studies that have been conducted on the Iranian response in the Gulf, and takes into account the response capability of Iran's ally Syria and that of Iran's Lebanese and Palestinian proxies. In addition, this paper makes four policy recommendations to reduce the possibility of regional escalation, which in any case is unlikely, considering the interests of the relevant actors. The main conclusion is that the possiblity of a strike against Iran is a pivotal instrument of diplomacy. A measured but credible use of this tool can help achieve the goals of the international campaign: to pressure Iran so that it agrees to concessions regarding its nuclear program, which will ensure that it does not possess military nuclear capabilities, and to reduce the likelihood of regional escalation.
See full text at The Institute for National Security Studies: If Attacked, How Would Iran Respond?