WASHINGTON -- One of the most infuriating problems in Iraq seems to generate precious little fury.

In a kind of malicious chemistry experiment, hostile powers are adding accelerants to Iraq's frothing chaos. Iran smuggles the advanced explosive devices that kill and maim American soldiers. Syria allows the transit of suicide bombers who kill Iraqis in markets and mosques, feeding sectarian rage.

This is not a complete explanation for the difficulties in Iraq. Poor governance and political paralysis would exist if Iran and Syria meddled or not. But without these outside influences, Tony Blair told me recently, the situation in Iraq would be "very nearly manageable."

America does not merely have challenges in the Middle East; we have enemies who contribute to the deaths of our troops. Yet Americans have shown little outrage, and the military reaction has been muted.

A stronger response would be justified, but the choices are neither obvious nor easy.

Iran, the main strategic threat, has two conflicting tendencies: It doesn't want long-term chaos in neighboring Iraq, but it wants America to decisively fail there. The second tendency is currently ascendant because the Iranians are hopeful that America is on the verge of a humiliating collapse of will -- for them, an irresistible source of immediate pleasure. So Iranian paramilitary groups train and arm radical Shiite militias, and provide explosive devices that also find their way to radical Sunni groups.

Engagement and deft diplomacy are not likely to change the Iranian interest in American defeat. Iran would require an unacceptable inducement to bail out American interests in Iraq: permission to proceed with its nuclear program. America would purchase tactical advantages in Iraq at a tremendous price -- a strategic nightmare in the entire Middle East.

Additional economic pressures on Iran and its proxies would increase the cost of its current course. This week President Bush issued an executive order financially targeting groups and individuals that recruit and send terrorists to Iraq. But any real leverage in this area will require the Europeans to take actions of their own.

There are also more straightforward approaches. Earlier this year, President Bush announced a dragnet directed at Iranian paramilitary activity in Iraq, and the troop surge has taken on the radical militias more directly. Further action might involve stepping up raids against Iranians in Iraq who exploit legitimate jobs as cover.

Beyond Iraq's borders, the options become difficult: engaging in hot pursuit against weapon supply lines over the Iranian border, or striking explosive factories and staging areas within Iran. This sort of escalation is opposed both by the Iraqi government and by American military leaders. The Department of Defense fears what is called "escalation dominance" -- meaning that in a broadened conflict, the Iranians could complicate our lives in Iraq and the region more than we complicate theirs. Continued...