By Phil Stewart and Jeff Mason WASHINGTON (Reuters) -U.S. Defense Secretary Lloyd Austin said in a statement on Saturday that he took “full responsibility” for secrecy surrounding an ongoing, week-long hospitalization for a still unspecified medical condition. Austin, who is 70, was admitted on New Year’s Day to Walter Reed National Military Medical Center for what the Pentagon has said were “complications following a recent elective medical procedure,” a fact the Defense Department kept under wraps for five days. The top Republican on the Senate Armed Services Committee, Senator Roger Wicker,…