Rumsfeld and General Richard Myers, chairman of the Joint Chiefs of Staff, were quizzed on Wednesday at a Senate hearing about the plans for the $42 million upgrade of the controversial detention centre.
"The detention facility upgrades, I am told, that you see in the budget for Guantanamo, are to meet Geneva Convention standards," Rumsfeld said.
"And since, as the general says, its not knowable how long they will be there, what we are doing is carrying out a US government policy that exists and trying to do it to the best extent it can be done," he said.
Myers said some prisoners will be held at the detention centre for the long-term.
"What we are doing is transitioning to a long-term detention mission, because there are some there that are bad enough that you do not want to release them," he said.
"And so they are going to have to be detained in some location. And no matter how the courts come out, that's probably going to be the location," Myers said.