BEIRUT -- America's decision to target Iranian agents in Iraq who may be involved in supporting violent militias is but another sign of the massive influence Iran is exercising in that troubled country. But the United States in fact facilitated Iran's growing influence by toppling Saddam Hussein's regime and that of the Taliban in Afghanistan, thus removing two factors that had kept the Iranian regime hemmed in for the last two decades. Moreover, high oil prices have filled the national treasury and Iran is benefiting from the opportunity created by America's being bogged down in Iraq and the growing international weight of Russia and China.

Iran is also reaping the returns of long-term investments. It has supported Iraqi Shiite groups since the early 1980s and has an equally long-standing alliance with Syria. In Lebanon, Iran helped create Hezbollah, which recently survived a head-on war with Israel and is the leading opponent of the anti-Syrian, Western-backed government. Iran's investment in Palestine is more recent, but its backing for the Hamas-led government, which has been frustrated elsewhere, is no less significant. A country of 70 million, Iran also has potential influence with Shiite communities in Kuwait, Saudi Arabia, Bahrain and the United Arab Emirates.

Iran's rise is causing alarm in the Arab Middle East, particularly in Saudi Arabia and Jordan, but also in Egypt. Though a Shiite country in an overwhelmingly Sunni region, Iran's radical Islamism resonates with the politicized Islamism that is energizing most Arab opposition movements, and its militant opposition to the U.S. and support for groups that engage Israel in battle is very popular on the Arab street and in the Arab media. At another level, Iran's rise, reinforced by its suspected bid for nuclear weapons threatens to awaken historical hostilities, between Sunnis and Shiites and between Persians and Arabs.