Davaan Ingraham / REUTERS
Hagel's comments came during an interview with CNN Wednesday afternoon, hours after President Barack Obama used the same phrase to describe the mission but subsequently walked back his comments and said he wanted to get the group to "the point where it is a manageable problem."
"It's not contain," Hagel said of the U.S.'s mission against ISIS. "It's exactly what the president said: Degrade and destroy."
Hagel said the Pentagon was preparing options for Obama to "degrade and destroy" ISIS, including inside Syria.
"Our mission ... is to provide him those options and those plans to accomplish the mission of destroy and degrade the capability of ISIS," said Hagel.
AP President Barack Obama speaking in Estonia on September 3, 2014. 
Hagel urged Wednesday that ISIS was a threat that needs to be taken seriously and could eventually pose a danger to American interests both abroad and in the U.S. However, he declined to specifically describe when he believed the group would pose an immediate danger.
"We have acknowledged publicly we are aware of over 100 U.S. citizens who have U.S. passports who are fighting in the Middle East with ISIL forces," said Hagel, "There may be more, we don't know, we can't take a chance ... on saying, well, let's technically define this, 'Is it a real threat today or tomorrow?'
As he has before, Hagel described the group as unprecedented in their brutality. He said they are "better organized" and "better funded" than any other terrorist group the U.S. has encountered, and he estimated they already control half of both Iraq and Syria.
"This crowd is a dangerous crowd," Hagel said. "They are an army. ... We better be taking them seriously."
Hagel concluded the interview by reiterating the U.S. objective is to "destroy" the group.
"We will do everything possible that we can do to destroy their capacity to inflict harm on our people," he said.