The Washington Post, May 21 - Since the collapse of Saddam Hussein's regime, Iran has methodically built and strengthened its military, political and religious influence in Iraq. Iran's Revolutionary Guard has extensively infiltrated Iraq's Ministry of the Interior and police force, both mainstays of Shiite power. The hundreds of Iranian mullahs and businessmen who have slipped across the border have a commanding presence in southern Iraq's commercial and religious sectors….

Over the past three years, Tehran has deployed to Iraq a large number of the Revolutionary Guard's Qods Force -- a highly professional force specializing in assassinations and bombings -- as well as officers from the Ministry of Intelligence and National Security and representatives of Lebanese Hezbollah.

The Qods Force has a longstanding relationship with Hezbollah, which it trains and supplies in coordination with Syria through an Islamic Revolutionary Guards Corps unit in central Lebanon. In the words of Iranian Maj. Gen. Yahya Rahim Safavi, the IRGC commander, "The range of [the IRGC's] duty is not limited to our land and we have extra-border missions."

Iranian personnel have established safe houses throughout southern Iraq. They monitor the movement of coalition forces, tend weapons caches, facilitate cross-border travel of clerics, smuggle munitions into Iraq and recruit individuals as intelligence sources. Presumably, Tehran has recruited networks within U.S. military bases and civilian compounds that could be activated on short notice. Iran is also believed by regional intelligence agencies to have armed and trained as many as 40,000 Iraqis to prevent an unlikely rollback of Shiite control.

Coalition forces have suffered the consequences of Iran's military presence. U.S. and British officials contend that the IRGC has introduced into Iraq "shaped charge designs" -- powerful bombs that channel the force of an explosion into a narrow path. (Lebanese Hezbollah also has used such bombs effectively against Israeli tanks.) According to the British, at least 10 of their soldiers in southern Iraq have been killed since May 2005 by the combination of such explosives and remote triggering devices. Marine Gen. Peter Pace, chairman of the Joint Chiefs of Staff, noted in a March briefing with Defense Secretary Donald H. Rumsfeld that these makeshift bombs are "traceable back to Iran."…

Iran's clerical regime could complicate matters for Washington even more by pressing its Shiite allies in Iraq to demand a U.S. withdrawal. The leading Shiite cleric in Iraq, Ayatollah Ali Sistani, has counseled patience and refrained from challenging the U.S. military presence; he is also wary of Tehran's influence over Iraqi politics. However, Abul al-Aziz al-Hakim, the head of the Supreme Council for the Islamic Revolution in Iraq, has closer ties to Tehran and has publicly chastised Washington for not tackling the Sunni insurgency. (The council's armed wing, the Badr Organization, musters thousands of armed members.) And the Mahdi Army of Moqtada al-Sadr also receives subsidies from Iran….

Tehran is capable of wreaking havoc in Iraq, and it may consider such a move in response to a U.S. attack. However, as Iraq continues its descent into chaos, Tehran must balance its desire to hurt the United States with the equally compelling objective of fostering an orderly transition to Shiite rule in Iraq.