By Phil Stewart
WASHINGTON (Reuters) - A U.S. missile defense system that is too robust could actually backfire and become destabilizing, prompting countries like China to expand their nuclear arsenals, a U.S. general said on Tuesday.
Air Force General Kevin Chilton, commander of the U.S. Strategic Command, did not question the current system, which was revised by President Barack Obama and the Pentagon in September.
But he explained that careful calculations would be needed when boosting U.S. defenses in the future to guard against threats from countries like North Korea.
"We have to be cautious with missile defense. Missile defense can be destabilizing depending on how you array it," Chilton told a defense gathering in Washington.
He outlined a scenario that he said "I don't think any of us want to see" in which hundreds of interceptors were deployed along the Western side of the United States.
"That kind of makes you feel more secure, doesn't it? But what would it make the Chinese think about their deterrent?" Chilton asked.
"That might encourage them to in fact double, triple, quadruple their current nuclear forces. Because they would feel that their deterrent was no longer viable."
Republican critics say Obama's decision to refocus U.S. missile defenses in Europe on Iranian short- and medium-range missiles could leave the U.S. mainland and parts of Western Europe more vulnerable to attack from an Iranian intercontinental ballistic missile, or ICBM.
But the Pentagon has assured that the 30 ground-based interceptor missiles to be deployed in Alaska and California by the end of 2010 will provide the United States with full protection against an Iranian ICBM.
Chilton said missile defense was crucial against countries like North Korea and Iran because they might not fear the U.S. threat of retaliation -- rendering the U.S. deterrence strategy used against Russia during the Cold War ineffective.
"It's not clear that pure nuclear might or conventional might would deter them if they had the ability to (strike) the United States or an ally, a friend in the region, with a nuclear-capable missile," Chilton said.
"That's the compelling argument for missile defense."
(Editing by Doina Chiacu)