WASHINGTON — The former director of the Centers for Disease Control and Prevention accused top federal health officials on Wednesday of excluding him from discussions in early 2020 about whether the coronavirus was the result of a laboratory leak — an assertion that one of the officials, Dr. Anthony S. Fauci, later said had “nothing to do with reality.” Three years into the pandemic, the accusation by the former C.D.C. director, Dr. Robert R. Redfield, put a spotlight on the lingering bitterness and partisan divisions around the scientific question of…