Gen. David Petraeus, the Iraq war boss, is telling surge troops that they will not be kept past their 15-month tours. That means the troop drawdown could begin in April, when the first troops in the surge will reach their 15th month on the ground. Officials say that all of the surge brigades reach their 15th month by August 2008. The timing is reflected in the developing "Petraeus plan." But associates say he's keeping his cards very close, not even revealing them to his top advisers, in case changes are required.