His West Germany career had started early with youth internationals in his years with Wormatia Worms. His first senior cap was a product of Helmut Schön looking for Sepp Maier replacements and the good form of young Kargus for Hamburg in the Bundesliga. Four days prior to Christmas 1975 Kargus was chosen to represent West Germany in a friendly against Turkey. He did well and was subsequently named in the 1976 UEFA European Championship squad, serving as (the unused) deputy of Sepp Maier. A further friendly appearance later, Kargus came on also at half-time against Yugoslavia in 1977 to replace Maier. That was the last cap (of three) Kargus won in his career, although he was one of three goalkeepers in the West German squad for the 1978 FIFA World Cup.