What’s the fastest growing American military mission overseas?

Hint: It’s the very mission the Bush administration once disdained the most.

The U.S. military is getting ever more enmeshed in peacekeeping, peace enforcement and nation-building around the world. There are 150,000 U.S. troops in Iraq, 11,500 in Afghanistan, and several thousand more in Bosnia and Kosovo. And, as President Bush travels around Africa, he’s pondering whether to send troops to stabilize war-torn Liberia.

Yet peacekeeping and nation-building are the missions for which U.S. forces are least prepared.

From the time the Bush administration came to power, it opposed peacekeeping missions. Early this year, Secretary of Defense Donald Rumsfeld endorsed the closing of the Army War College’s Peacekeeping Institute in Carlisle, Pa., the only government body dedicated to the study of peacekeeping.

Condoleezza Rice, Bush’s national security adviser, wrote in Foreign Affairs in January 2000 that the U.S. military was meant to be a lethal instrument and “not a civilian police force. It is not a political referee. And it is most certainly not designed to build a civilian society,” she added firmly. U.S. intervention in “humanitarian” crises “should be, at best, exceedingly rare.”

So how did it come to pass that 19-year-old enlistees are patrolling slums in Baghdad, while U.S. troops remain in the Balkans and may go to Liberia?

Chalk it up to the aftershocks of 9/11.

Once international terrorism became the main threat to American security, Bush officials had to reassess the risk of leaving failed states to fester. A U.S. pullout in Afghanistan would undercut the fragile government of Hamid Karzai and encourage the return of Islamists. The U.S. military in Iraq must now help stabilize a badly fragmented nation or risk a dangerous chaos.

As for Liberia, if the administration sends in U.S. troops, the reason will be a combination of embarrassment and new security concerns. Liberia’s awful ruler Charles Taylor has not only wrecked his own country but also fueled civil wars across West Africa – for example, by aiding thuggish militias in Sierra Leone that chopped off the limbs of thousands of children.

Having cited humanitarian concerns as a prime reason for the Iraq war, it’s harder for Bush to ignore such concerns in an African state founded by former U.S. slaves. In addition, Taylor-sponsored chaos across West Africa now raises concerns about creating new, terrorist-prone neighborhoods. And there is a precedent whereby small British and French forces brought a modicum of stability to, respectively, neighboring Sierra Leone and Cote d’Ivoire.

But, although it is now immersed in peace enforcement and nation-building, the administration still isn’t giving its troops the proper training to do the job. U.S. forces in Baghdad don’t have experience with rough urban policing, where one minute children are crawling on tanks and the next someone is shooting at you.

They don’t have the counterinsurgency training British troops got in Northern Ireland. Nor are there anywhere near enough military specialists in civilian affairs, leaving regular U.S. enlisted men trying to run small Iraqi towns.

The Pentagon knows it has a shortage of trained peacekeepers and peace enforcers but so far seems unwilling to confront the problem realistically. There have been efforts to recruit troops from allied countries – ranging from the Philippines to Azerbaijan – to do Iraq peacekeeping mop-up. But so far, those efforts haven’t been very successful. Anyway, such a melange of forces isn’t likely to do an effective job.

Defense Secretary Donald Rumsfeld is said to be discussing the idea that the United States would organize a standing international peacekeeping force outside the United Nations, led by U.S. Army troops trained for the job.

It’s all to the good if Rumsfeld is entertaining the need to train U.S. forces for the task of stabilizing broken countries. (Plans to close the Peacekeeping Institute were put on hold this week.)

But why reinvent the wheel? There have been proposals for a U.N. peacekeeping force composed of on-call units from countries with capable armies. Isn’t this idea worth some consideration, especially since many of these countries would contribute troops only to a U.N. force?

Like it or not, the Pentagon is being cast by U.S. policy in the role of peacekeeper as well as warmaker. It should be looking widely for all the help it can get.

Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer.