By Phil Stewart and David Alexander WASHINGTON (Reuters) - U.S. Defense Secretary Chuck Hagel announced plans on Friday to bolster U.S. missile defenses in response to "irresponsible and reckless provocations" by North Korea, which threatened a preventative nuclear strike against the United States last week. Hagel said the Pentagon would add 14 new anti-missile interceptors at Fort Greely in Alaska - an effective reversal of an early Obama administration decision - and move ahead with the deployment of a second missile-defense radar in Japan. ...