(Reuters) - Leaders battling for promotion in China's Communist Party are using pages out of an old manual for negotiating the rungs of power, with the launch of separate probes that have tarnished the chances of one rising star and burnished those of another.

While circumstances are murky, the twin cases have rapidly exploded to upset a leadership succession that just weeks ago had been plodding along smoothly.

With the Communist Party's 18th Congress just months away, the sudden downfall of two officials -- one a right-hand man to a rising leader, the other the target of a rising general -- has increased the stakes, revved up the rumormill and added a strong hint of political uncertainty to the most critical leadership transition in China in nearly a decade.