JUDGMENT ON DELTCHEV [247 pp)
Eric AmblerKnopf ($3).
Eric Ambler can make more fictional sense out of Balkan intrigue than anybody now writing. In the late '305, when he last tried, he produced four of the neatest suspense stories of the decade: Background to Danger, Cause for Alarm, A Coffin for Dimitrios, Journey into Fear. What with the war (he wound up a lieutenant colonel), and scripting and producing postwar movies for J. Arthur Rank, Englishman Ambler has been pretty busy since those days. But he has managed to write another Balkan thriller, a fact for which Ambler fans can duly rejoice.