By Howard Schneider and Lindsay Dunsmuir WASHINGTON (Reuters) -Federal Reserve Chair Jerome Powell, balancing high U.S. inflation against the complex new risks of a European land war, said Wednesday the central bank would begin “carefully” raising interest rates at its upcoming March meeting but be ready to move more aggressively if inflation does not cool as quickly as expected. Powell called the Russian invasion of Ukraine “a game changer” that could have unpredictable consequences. “There are events yet to come and we don’t know what the real effect on the U.S. economy will be,” Powell told…