WASHINGTON – A former CIA officer and Afghanistan expert told a Senate panel Wednesday that sending more troops to Afghanistan would hurt American interests, but the former head of the CIA Counterterrorism Center argued that al-Qaida would return without a “significant” U.S. presence.

The Obama administration is reviewing its Afghanistan strategy in light of Gen. Stanley McChrystal’s reported recommendation to add as many as 40,000 more troops. Proponents of an increase argue that maintaining the status quo or reducing the number of troops would result in the Taliban returning to power in Afghanistan and al-Qaida resuming operations there. But opponents say a more narrow focus on denying a safe haven to al-Qaida would require fewer troops and be more likely to achieve success.

Following McChrystal’s advice “will be most costly in terms of blood and treasure and probably the least likely to succeed,” Marc Sageman, a senior fellow at the Foreign Policy Research Institute, told the Senate Foreign Relations Committee.

Sageman, who worked with the Afghan mujahedin while in the CIA, said that if NATO troops were to withdraw completely from Afghanistan, it’s not certain the Taliban would recapture Afghanistan, as some critics fear. “It took more than three years for (a) much better armed and far more popular insurgency to capture the power after the complete withdrawal of the Soviet forces in Afghanistan 20 years ago,” he said.

He also warned that an increase in U.S. troops would alienate Afghans and raise the threat of terrorism in the U.S. due to “the inevitable increase of killings of Muslims by Western forces” that would result from higher troop levels.

But Robert Grenier, a former CIA agent who headed the agency’s Counterterrorism Center and worked in Pakistan, said that even if President Barack Obama chooses the more limited, counterterrorism approach, the U.S. would “still need a significant presence” In Afghanistan.

Although al-Qaida no longer has a significant presence in Afghanistan, preventing it from returning and establishing operating bases would require more U.S. forces, he said.

While both men said gaining the trust of local tribal leaders and even warlords is an important factor in securing Afghanistan from becoming an al-Qaida safe haven under Taliban control, they disagreed on the strategy to achieve the goal.

Grenier reiterated his belief that more troops are needed whether the goal is limited to denying a safe haven in Afghanistan to terrorists or the larger goal of establishing a government and providing security for Afghan citizens.

But Sageman maintained that an increase in troops would unite the Taliban, which he described as a fractious group that is incapable of marching on Kabul now but could be mobilized if a large American presence continues.