WASHINGTON — Earlier this year, President Obama likened the Islamic State in Iraq and Syria to a junior varsity basketball squad, a group that posed little of the threat once presented by Osama bin Laden and Al Qaeda.

But on Thursday, Defense Secretary Chuck Hagel called ISIS an “imminent threat to every interest we have,” adding, “This is beyond anything that we’ve seen.”

With the rapid advance of ISIS across northern Iraq, and the release this week of a video showing one of the group’s operatives beheading an American journalist, the language Obama administration officials are using to describe the danger the terrorist group poses to the United States has become steadily more pointed. But some American officials and terrorism experts said that the ominous words overstated the group’s ability to attack the United States and its interests abroad, and that ISIS could be undone by its own brutality and nihilism.

“They have a lot of attributes that should scare us: money, people, weapons and a huge swath of territory,” said Andrew Liepman, a senior fellow at the RAND Corporation and former deputy head of the National Counterterrorism Center. “But when we’re surprised by a group, as we have been in this case, we tend to overreact.”