WASHINGTON -- The U.S. is moving ground-to-air missile defenses to Hawaii as tensions escalate between Washington and Pyongyang over North Korea's recent moves to restart its nuclear-weapon program and resume test-firing long-range missiles.

Defense Secretary Robert Gates said on Thursday that the U.S. is concerned that Pyongyang might soon fire a missile toward Hawaii. Some senior U.S. officials expect a North Korean test by midsummer, even though most don't believe the missile would be capable of crossing the Pacific and...