If confirmed, Lumpkin would officially become the Pentagon's chief of special operations and low-intensity conflict (SO/LIC).
On Thursday, Sen. Kelly Ayotte (R-N.H.) pressed Lumpkin on whether he supported the administration's decision for a limited interrogation of al-Libi before handing him over to the Justice Department for trial.
"You would agree with me that it's best to take as much time as you need to interrogate someone that may have valuable information, to shed light on al Qaeda, and perhaps prevent future attacks?" Ayotte asked.
In response, Lumpkin said the "preferred methodology" would not to cap interrogations of terror suspects, particularly a senior al Qaeda leader like al-Libi.
"From an operational standpoint, that's the preferred methodology," Lumpkin said.
"As things flow ... you don't know necessarily what you're going to get, and you don't want to be up against a clock," he added.
Members of the Army's 1st Special Operational Detachment, also known as Delta Force, took the Libyan national into custody Saturday during a daylight capture mission in Tripoli.
U.S. military and intelligence officials are interrogating al-Libi aboard the USS San Antonio somewhere in the Mediterranean before remanding him into federal custody to stand trial.
Under the rules of war, al-Libi can only be held for up to 60 days aboard the Navy ship before being handed over to federal law enforcement.
But Ayotte and other Senate Republicans say 60 days would barely give interrogators time to scratch the surface of what al-Libi knows about the terror group.
They claim al-Libi should be sent to the military prison in Guantánamo Bay, Cuba, where American officials can interrogate the al Qaeda leader without any time constraints.
But Obama's desire to shutter the Cuba facility is denying U.S. intelligence a crucial opportunity to find out all it can about al Qaeda's operations, including possible future attacks, from al-Libi.
“In criminal [court] you are trying to solve a crime — in war, you are trying to defeat the enemy,” Sen. Lindsey Graham (R-S.C.) told reporters earlier this week.
For her part, Ayotte said it would be “absolutely unacceptable” if the chance to interrogate al-Libi were sacrificed in pursuit of Obama’s first-term promise to close the prison.
During the hearing, Lumpkin made clear to Ayotte his office had no involvement or insight into the al-Libi operation and ongoing interrogation.
"On these particular operations, I can provide no granularity or fidelity," the nominee told Ayotte.
That said, "I'm always hesitant on timelines," Lumpkin added.
However, U.S. military and intelligence officials claim they could keep al-Libi indefinitely, despite White House plans to have him handed over to the federal courts for trial.
"It doesn't matter the length of time as long as [he's held] in a humane condition," a U.S. official told Reuters Wednesday.