West Berlin — ''I started as a black marketeer,'' says Emil Janucek proudly. ''How else could someone like me earn a living then?'' The year was 1946 and the place was Berlin. Emil Janucek, now ''Germany's largest trader with the East bloc,'' in the words of the West German financial magazine Capital, was a 24-year-old survivor of Auschwitz, Dachau, and Sachsenhausen.
Hitler had ruined his plans to become a doctor. The war had interrupted his medical school education. A relative in America had not come through with promised financial help and a ticket to the United States.
So Mr. Janucek subsisted on petty smuggling, until he found the perfect entry-level position. Perfect, that is, if your career goal is to become an East-West middleman someday.
The job was to find out how employees were stealing cognac, cigarettes, and furs from the Soviet Army's warehouse. Janucek's employers - the generals at Russian Army headquarters at the Friedrich Hotel in the then-Soviet sector of Berlin - wanted to make sure that the luxury items did, in fact, get sent to well-placed Communist Party officials in Moscow.
''They had hired me to be an accountant. They quickly found out that I hadn't the slightest idea what it involved. But catching crooks - for someone like me, that was no challenge,'' Janucek says with a quick smile.
Today, Janucek says he has a $1.2 billion-a-year business. He has plugged into an enormous trade network. The seven East-bloc countries do an estimated $ 100 billion a year in trade with the 24 countries of the Organization for Economic Cooperation and Development, according to a recent estimate by West Berlin's Institute for Economic Research.
A few middlemen arrange much of this trade. The field is one of the last bastions of the dealer, the person who can parlay a few personal contacts and a knack for seeing the profit in the improbable into a fortune. In Janucek's case, that knack has resulted in a fortune estimated to be in the hundreds of millions of dollars, West German financial experts say.
Janucek is unique for the breadth of his trade. From his well-furnished office in West Berlin, he buys oil cheaply from the Soviets for a letter of credit, and then sells it back to them. He makes a profit each way, while the Soviets have both a letter of credit and the oil.
He imports tobacco from Zimbabwe, packages it under license from Western cigarette firms, then sells it in East Germany as a duty-free luxury item to bargain-hunters from the West. And as the East-bloc representative for Lever Brothers Company, he plays a large part in stocking the shelves of Budapest stores with Western toothpaste, cosmetics, and soap.
Other East-bloc middlemen generally choose to concentrate on a particular commodity. These include:
* Butter. Jean-Baptiste Doumeng is called the ''Red Billionaire.'' A member of the French Communist Party for more than 40 years, he profits from the European Community's albatross: the butter mountain.
Mr. Doumeng controls agricultural trade between France and the East bloc through his organization, the Union of Agricultural Cooperatives of the Southwest. Some 150,000 farmers and wine producers, 40 import-export firms, and several banks are associated with Doumeng.
There are 400,000 tons of EC butter in cold storage. The costs of milk subsidies are angering consumers and literally bankrupting the Community. Doumeng acquires butter at bargain-basement prices and sells it to the Soviets or developing countries - at a considerable profit.
* Atomic waste. Alfred Hampel of Dusseldorf, West Germany, started importing Soviet uranium into the West in the early '70s. Last October, he concluded a major deal with the People's Republic of China: For $6 billion, the Chinese will store 400,000 tons of waste from European nuclear power plants in the isolated Gobi Desert. The plans require the approval of the West European countries involved, as well as that of the supplier nations, Canada and the United States.
* People. Over 21 years, West Berlin attorney Jurgen Stange and his East Berlin colleague Wolfgang Vogel arranged the delivery of 20,000 East German citizens and political prisoners to the West. Mr. Stange's fee was a minimum of
Discredited by a scandal involving a missing 460,000 marks (about $180,000), his activities are at least temporarily at an end.
Not so Mr. Vogel, the East Berliner who helped arrange the transfer freeing the U-2 pilot Francis Gary Powers in 1962. Vogel has been busy wangling exit permits for East Germans who barricaded themselves in the US Embassy in East Berlin, as well as the family of Ingrid Berg, the niece of East German Premier Willi Stoph. The Berg family had taken refuge in the West German Embassy in Prague to dramatize its case.
Although other prominent middlemen, such as Hamburg weapons dealer Horst Cepanski, have gained notoriety through their dealings with the East bloc (in Cepanski's case, selling Bulgarian machine guns to Saudi Arabia and Soviet radar systems and tanks to Iran), Janucek is highly respected.
''He is a serious businessman,'' says Leo Grosskopf of the Berliner Marketing Organization. Mr. Grosskopf, one of the leading experts on East-West trade, uses ''serious'' in the German sense of the word: ''respected'' and ''worthy of being taken seriously.''
''I do a nice business,'' Janucek says modestly. With property in Germany and Austria, factories in Europe and Israel, he has come a long way from Auschwitz.