WASHINGTON, Nov 4 (Reuters) - Lael Brainard, a top economic diplomat at the U.S. Treasury, will step down from her post on Friday, a Treasury official said.

As undersecretary of the Treasury for international affairs since 2010, Brainard, 51, has played a key role in pushing China toward a flexible currency and pressing Europe to tackle its debt crisis more aggressively.

She reportedly has been under consideration to fill a vacancy at the Federal Reserve.