The top U.S. military officer says the Pentagon is scrambling to find trainers to send to Afghanistan. But it will be difficult to do that before commanders reduce U.S. troops in Iraq.

The quandary has left U.S. military leaders short in a region where they believe the next terrorist attack against the United States will form. Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said Tuesday that the mountainous border region between Afghanistan and Pakistan — where Osama bin Laden is rumored to be hiding — is the site of planning for the next attack.

Stemming that threat will depend largely on U.S. efforts to train the Pakistani military to fight along the border, and to quell the Taliban resurgence in Afghanistan. In both cases, trainers are critical.