By Richard Cowan WASHINGTON (Reuters) – U.S. House of Representatives Speaker Nancy Pelosi, the first woman to hold that powerful post, said on Thursday she will step down as the chamber’s Democratic leader as her allies prepared a passing of the torch to Representative Hakeem Jeffries. Pelosi, an 82-year-old liberal from California who has served two stints as speaker, said she will remain in Congress, representing San Francisco as she has done for 35 years. She made the announcement a day after Republicans secured a slim majority in the chamber following last week’s midterm elections. Jeffri…