GERMANY is still haunted by many ghosts from the dark years of Nazi rule, but few are as enduring or as strange as the specter of I.G. Farben.
Once the world's biggest chemical conglomerate, I.G. Farben played so important a role in Hitler's war machine and in the Holocaust that it came to be called ''the devil's chemist.'' It manufactured Zyklon B, the gas-chamber poison, among many other products, and its factories exploited more than 35,000 slave laborers, many from Auschwitz. It even built a concentration camp of its own to improve efficiency.
Allied officials broke up Farben after the war and distributed most of its assets to new companies. The old headquarters, a grim concrete fortress here, was converted into American military offices and is now being turned into university classrooms.