奥巴马通告周五全国纪念肯尼迪

President Barack Obama has ordered flags across the United States to fly at half staff to honor President John F. Kennedy -- assassinated 50 years ago Friday.

Mr. Obama called his revered predecessor an "extraordinary public servant" who had broad vision and sober idealism.  Mr. Obama laid a wreath at President Kennedy's grave at Arlington National Cemetery on Wednesday.

Church bells will ring in Dallas, Texas -- the southwestern city where President Kennedy was gunned down.  There will also be moments of silence and Pulitzer Prize-winning historian David McCullough will read from some of Mr. Kennedy's speeches.