In fact, it is the abilities that Mr. Kim is not showing off that have the Obama administration most worried. The cyberattacks on South Korea’s banking system and television broadcasters two weeks ago were surprisingly successful, as was the torpedo attack three years ago this week on the Cheonan, a naval corvette, that killed 46 South Korean sailors. The North has never acknowledged involvement in either — though the South believes it was responsible for both and so do American experts.

“We’re convinced this is about Kim solidifying his place with his own people and his own military, who still don’t know him,” one senior administration official said Friday. He added, “We’re worried about what he’s going to do next, but we’re not worried about what he seems to be threatening to do next.”

The cyberattacks and torpedo attack have something in common: Unlike the missile attacks and beach landings that Mr. Kim seems to be suggesting are imminent, they are hard to trace to North Korea, at least immediately. As a result, they are hard to retaliate against, and in fact the South never struck back militarily for the sinking of the Cheonan, even after a commission of inquiry, with experts from outside South Korea, concluded it was the work of a submarine-launched torpedo.

To North Korea experts in Washington and Seoul, there is something familiar in the country’s threats to “keep the White House in the cross hairs of our long-range missiles.” Such threat of armed brinkmanship — the catchphrase in the 1990s was that Seoul would become a “sea of fire,” a term recently revived by North Korea’s news agencies — has in the past drawn its adversaries to the bargaining table with economic concessions. But at the same time, the tensions with the outside world provide the government with opportunities to elevate its leader’s status among his people — which might be more important to a young, untested leader than it was to his father and grandfather.