WASHINGTON — The Defense Intelligence Agency is pulling together a group of analysts and experts to monitor competition with China, a world power Pentagon officials consider the leading threat to U.S. national security. John Kirchhofer, the DIA’s chief of staff , on Nov. 29 said his agency, which produces, analyzes and disseminates military intelligence, established a “China mission group” that will reach full operational capacity early next year. “It’s as simple as this: We created a box and