Gates says he's been a supporter of the concept since the days of Ronald Reagan's Strategic Defense Initiative, dubbed "Star Wars" by its opponents.
But Gates says some of the current program was wasteful or unrealistic.
He told supporters of the system in Congress on Thursday that the U.S. doesn't need 14 more missile interceptors to defend against a technologically unsophisticated North Korea.
He says he's starting over with another troubled part of the system and making other changes. He didn't address plans to base part of the system in Europe.
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