Barack Obama is taking heat for hinting that he might refine his 16-month timetable for withdrawing U.S. troops from Iraq. But a forthcoming Pentagon-sponsored report will recommend an even steeper drawdown in less time, NEWSWEEK has learned. If adopted, the 300-page report by a defense analysis group at the Naval Postgraduate School in Monterey, Calif., could transform the debate about Iraq in the presidential election.