BEIJING -- China's exports slowed dramatically last month and imports plummeted, highlighting the effects of the global slowdown on the world's third-largest economy and the failure of its stimulus program to gain traction so far.

Exports in January fell 17.5% from a year earlier and imports dropped 43.1%, according to Chinese government data released Wednesday. That boosted the country's trade surplus -- at the center of recent criticism from Washington -- to $39.11 billion.

Economists...