WASHINGTON — A briefing paper prepared for British Prime Minister Tony Blair and his top advisers eight months before the U.S.-led invasion of Iraq concluded the U.S. military was not preparing adequately for what the British memo predicted would be a "protracted and costly" postwar occupation of that country. The eight-page memo, written in advance of a July 23, 2002, Downing Street meeting on Iraq, provides new insights into how senior British officials saw a Bush administration decision to go to war as inevitable.