The congressional investigation of Communists turned last week from a story of espionage to a story of Communists in high places in Government. The course was changed by the testimony of a soft-voiced ex-Communist, who sat down before the House Un-American Activities Committee and calmly told a tale of high powered plotting in New Deal days.He was Whittaker Chambers, 47, for 13 years a member and “paid functionary” of the Communist Party, a strong anti-Communist since 1937