If the Pentagon were ever to get courts’ leeway to withdraw a pledge not to seek the death penalty, the United States says, it should be for the alleged mastermind.

The federal government agreed not to seek the death penalty in a plea deal with Khalid Sheikh Mohammed, the alleged mastermind behind the 9/11 terror attacks — but tried to back out just days later.

Judges heard nearly four hours of arguments over whether former Defense Secretary Lloyd Austin had the authority to unwind plea deals reached with three men accused of planning the Sept. 11, 2001, terror attacks.