The Obama administration has conducted a vigorous internal debate over its new strategy for Afghanistan, expected to be unveiled by the president in a speech Friday. According to two U.S. government sources close to the issue, senior policymakers were divided over how comprehensive to make the strategy, involving an initial boost of 17,000 U.S. troops. On the one side were Vice President Joseph R. Biden Jr. and Deputy Secretary of State James B. Steinberg, who argued in closed-door meetings for a minimal strategy of stabilizing Afghanistan that one source described as a "lowest common denominator" approach. The goal of these...