WASHINGTON ― The argument within the Obama administration for a big troop withdrawal from Afghanistan over the next year goes roughly like this: We’ve killed Osama bin Laden. That means we’ve achieved the core goal for which we sent forces in 2001. We have a ticket out, and we should take it. 

The counterargument from administration hawks is that a quick departure is a guarantee of failure. It risks repeating the mistake the United States made in the 1980s when, after pumping money and guns into Afghanistan to defeat the Soviet Union, America walked away ― creating a power vacuum that was exploited by warlords and their regional patrons.

Somewhere in the middle is President Obama. “We will begin a transition this summer,” he said Monday. “By killing bin Laden, by blunting the momentum of the Taliban, we have now accomplished a lot of what we set out to accomplish 10 years ago.” But he didn’t say what that would mean in terms of policy.

Inevitably, this debate is partly a numbers game: The rapid-withdrawal advocates want a timetable for removing all 30,000 of the “surge” troops Obama decided to send in December 2009. The “stay the course” proponents want a modest reduction of 3,000 to 5,000 troops, which is all they think conditions allow. A “split the difference” caucus argues for a cutback that hits five figures ― something around 10,000.

The problem with all these arguments is that they lack a clear strategic rationale. Do the “stay the course” proponents really expect that the Afghan army will be strong enough to stand on its own by 2014? That strikes many analysts as a dubious proposition.

Are the speedy-withdrawal advocates really comfortable with an Afghanistan that could quickly return to the pattern of the 1990s, with the regional powers, India and Pakistan, each manipulating their favorite ethnic groups and warlords? That sounds like a recipe for perpetual instability in South Asia.

The point is obvious: The number of troops withdrawn should be a function of the strategic plan, not the other way around. The three variables that U.S. policymakers have been discussing ― troop withdrawal, reconciliation with the Taliban and drone attacks in Pakistan ― are interrelated. What effect will a change in one variable have on the others?

Let’s take the question of political reconciliation: If Obama announces a big troop withdrawal, will this encourage Taliban concessions? Probably not, unless the Taliban is a charity organization in disguise. A skeptic about reconciliation (as Vice President Joe Biden is said to be) could argue for a pullout, regardless of its effect on diplomacy. But if you think negotiation may work, then you want military leverage that enhances it.

The administration has begun secret talks with Taliban intermediaries. If this process is serious, it needs to move toward the practical test of a cease-fire, perhaps initially in one locale: The U.S. needs to show the Taliban there’s a way to ease the pain through negotiations, and Taliban representatives need to show they can deliver on the ground.

The same pragmatic test should be applied to Predator drone attacks. The drones have been an invaluable weapon against al-Qaeda, reaching into the North Waziristan safe haven. But if the drone attacks cause such severe political problems for Pakistan that they prevent Islamabad from playing a constructive role in reconciliation, then the policy may need adjustment. This argument has been advanced by Cameron Munter, the U.S. ambassador to Pakistan, and some military officials, such as Adm. Mike Mullen, the chairman of the Joint Chiefs, also seem interested in thinking about the drone attacks in cost-benefit terms.

The White House has discussed the drone-attack conundrum, but for now doesn’t plan any change in U.S. policy. The hope is that improved counterterrorism cooperation with Pakistan will lead to better targeting by the drones and more use of alternative tactics.

The strategic goal is a regional framework for a post-America Afghanistan. That means, in essence, a coordinated effort by Pakistan, India, Afghanistan and the U.S. to make a political settlement work. Obama’s challenge in framing his troop-withdrawal announcement is to enhance this regional process, not undercut it. The leaders of Afghanistan, Pakistan and India all want American troops to go home ― but not if that creates a new vacuum that makes them more vulnerable.

“We’re not going to do anything precipitous,” Obama said Monday, in a statement that embodied his governing style. Hopefully, this means an exit strategy that actually provides a reliable exit.

By David Ignatius

David Ignatius’ email address is davidignatius@washpost.com ― Ed.

(Washington Post Writers Group)