The battle for Marja in southern Afghanistan is the first test of whether the Afghan national army is ready for prime time.

Yet reporting from Marja indicates that while Afghan army troops have shown courage, U.S. Marines have done all the heavy lifting. “Fledgling Afghan army units … follow behind the Americans and do what they are told,” said the New York Times.

It seems unlikely that the Afghan army can operate alone anytime soon. But President Obama has said U.S. troops will start a drawdown in 2011. So what does Marja tell us about whether that deadline is real?

The key to a responsible U.S. departure, says John Nagl, a co-author of Gen. David Petraeus’ counterinsurgency manual, is “the creation of some kind of Afghan force that can secure the country after we leave.” He added, “We can reduce the effectiveness of a lot of Afghan Taliban, but we can’t ultimately create a secure Afghanistan without training Afghan security forces.” Yet it was not until late last year that the U.S. government got serious about training Afghan troops, says Nagl, now head of the Center for a New American Security.

My two visits last year to the Kabul Military Training Center, where U.S. and Afghan trainers work with Afghan recruits, gave me a feel for the daunting nature of the task. The Afghan army is on track to meet its goal of 134,000 troops by October, but quality — not quantity — is the issue. A graveyard of rusted Russian tanks strewn across one part of the vast training grounds, which were once used by the Soviets, reminded me of past military mistakes.

In November, I watched Afghan officers instruct new troops on how to enter an urban building to check for enemy fighters. The building was delineated with rocks on a flat field. Afghan Sgt. Amanullah Khayar warned the troops to check for hidden wires and booby traps before they charged into the “building.”

Khayar told me 15 to 20 percent of his soldiers are illiterate. Besides their eight-week course, they got literacy training, along with a three- to 12-week driving course meant to reduce the number of casualties caused by novice drivers. The troops have a high attrition rate, although a recent pay increase may help address that, along with extra pay for serving in combat zones.

Some Afghan officers complained to me about preferences given to Tajiks over Pashtuns, who are the largest Afghan ethnic group and the one from which the Taliban come. Defense Minister Abdul Rahim Wardak told me he’d made ethnic balance a priority, with percentage targets for each brigade. And Sgt. Khayar instructed the troops in both Dari (the Tajiks’ language) and Pashto. The Afghan Uzbeks were on their own.

U.S. officers at the base spoke of another huge problem: a woeful shortage of Afghan trainers and a serious shortage of U.S. mentors to oversee them. Sometimes there are only two mentors to an Afghan battalion of 1,200. The U.S. commander, Gen. Stanley McChrystal, has urged the NATO allies to commit 2,000 new instructors, with little result so far.

The uncertainties that dog the training program lead many to conclude that Afghan security must be sought elsewhere: with local militias, or with programs to woo away Taliban fighters. In the short term, both factors are key to shifting the battlefield momentum.

But when it comes to long-term stability, the training of the Afghan army is still crucial. To understand why, it helps to look back at our training of Iraqi army troops.

That, too, was a lengthy and difficult process, with critical mistakes made, such as totally dismantling the old Iraqi army. There was a shortage of trainers, and U.S. officials often overestimated the rate of progress. And there, too, tribal militias played a key role in pushing insurgents back.

But once the heavy fighting was done, the Iraqi army found its nerve and began to cohere, incorporating some irregular fighters. Despite ongoing ethnic tensions within, the Iraqi army has grown into an important national institution that has accumulated public trust.

Something similar could happen in Afghanistan, with NATO troops and tribal forces turning the tide, and Afghan units playing a bigger role once the momentum shifts and U.S. troops begin to draw down.

“This is going to take longer and be harder than anyone is saying right now,” said Nagl, who thinks it will take five years for the Afghan army to jell, “but it is our exit strategy if we want to leave behind a stable Afghanistan.” The time for NATO to cough up those 2,000 new trainers is now.

— Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer. trubin@phillynews.com