Aug 21 (Reuters) - U.S. Treasury Secretary Janet Yellen has told senior White House advisers she backs reappointing Jerome Powell as U.S. Federal Reserve Chair, a Bloomberg News reporter wrote on Twitter here. President Joe Biden has not made a decision and will likely weigh in around Labor Day in early September, the reporter added in the tweet. (Reporting by Aakriti Bhalla in Bengaluru; Editing by Will Dunham) Our Standards: The Thomson Reuters Trust Principles.