President Barack Obama deserves credit for conducting a thorough review of U.S. aims in Afghanistan and Pakistan, and for adapting means and ends. Rather than an indefinite military mission with large numbers of U.S. troops, a key component of Obama’s strategy announced last week is to increase assistance and training of Afghan forces to ensure the Afghans do not become dependent on foreign troops for their security.

Left unanswered in the president’s plan is the number of U.S. troops that will ultimately be deployed in support of his new strategy. Classic counterinsurgency doctrine would call for several hundred thousand security personnel in a country the size of Afghanistan. In Senate testimony on April 1, chief of U.S. Central Command, General David Petraeus, disclosed that American commanders in Afghanistan have requested 10,000 more troops to help fight the Taliban. “If you assume there is an insurgency throughout the country,” Petraeus told the panel, “you need more forces.”

The President should strongly resist any calls to add more troops. With the increases announced last Friday, along with those already programmed, the U.S. military presence will exceed 60,000 by summer. That is more than enough troops to carry out the focused mission of training Afghan forces and building the Afghan government’s ability to secure their country.

Obama’s plan to continue building up the Afghan National Army (ANA) to 134,000 does not go far enough, but it is a step in the right direction. Afghan Defense Minister Abdul Rahim Wardak wants to increase the number of police officers, commandos, and border guards to bring the total number of Afghan security forces to 400,000. Maintaining a force that large would alone cost from $10 billion to $20 billion over the next six or seven years. For 2008, Afghanistan’s GDP was $12.85 billion.

The security services, including the undermanned and poorly equipped Afghan National Police, must develop their capabilities across tribal and ethnic lines. Many Pashtun, Uzbek, Hazara, and Tajik security personnel have stronger loyalties to families, tribes, clan and ethnic groups than to the unifying force of an army or police unit.

Americans will be essential partners for the Afghans. But our assistance must be targeted, results-based, and tied to clear, achievable metrics. Benchmarks should include determining how many Afghan security forces can operate independent of coalition forces and ensuring that Afghans take the lead in land-based military operations so that Western forces can eventually take a back seat.

Equally significant to bolstering Afghan security forces is the narrowed focus on al Qaeda and the circumstances in neighboring Pakistan. Since 2001, al Qaeda has shifted its leadership across the border into that country’s rugged northwest, where the United States does not have (and should not have) a large military footprint.

Washington has only limited leverage over Islamabad. It still relies on Pakistan for the security of its supply lines into Afghanistan and for intelligence on militant activity along its border. An attack this past weekend on a police training center in Lahore, in eastern Pakistan, hundreds of miles away from the Afghan border, was reportedly carried out Baitullah Mehsud’s Tehrik-e-Taliban Pakistan, a tribal-based militant group possibly behind the assassination of Pakistani politician Benazir Bhutto. This attack highlights that Islamabad’s loss of control in the tribal areas now threatens the Punjabi heartland. It also underscores the importance (and budding opportunity) for Obama to work more closely with Pakistan’s civilian and military leaders who may finally come to appreciate the urgent need to eliminate violent extremism throughout their country.

As the war in Afghanistan rages on, Obama should be skeptical of any suggestions that the defeat of al Qaeda depends upon a massive troop presence. Globally, the United States has degraded al Qaeda’s ability to pull off another 9/11 by employing operations that look a lot like police detective work. Most of the greatest successes scored against al Qaeda, such as the snatch-and-grab operations that netted Khalid Sheik Mohammed and Ramzi bin al Shibh, have not relied on large numbers of U.S. troops. Intelligence sharing and close cooperation with foreign law enforcement and intelligence agencies have done more to round up suspected terrorists than blunt military force.

Committing still more troops to Afghanistan would only weaken the authority of Afghan leaders and undermine our ability to deal with security challenges elsewhere in the world.