ORDOS, China—For a sense of the sharp policy shift China's leaders have to orchestrate to avoid the world's second-largest economy landing with a hard thud, look no further than this Inner Mongolia desert town, where construction cranes have come to an abrupt standstill.

Just as a European crisis and a weak U.S. recovery are hurting Chinese exporters, the confidence that had sustained China's property boom is evaporating, causing a double whammy for growth: fading demand overseas...