He estimated that at least 25 percent of the heroin being consumed in Western Europe was now passing through Eastern Europe, and he said that of the 30 tons of hashish seized in all of Europe this year, half had been found in Poland and Bulgaria.

At the moment, most of the drugs passing through Eastern Europe appear to be destined for users in Western Europe, but the United States is alert to the possibility that the drug traffickers will "exploit opportunities in the United States," Stephen Greene, acting administrator of the Drug Enforcement Administration, said in a telephone interview from Washington.

Washington is particularly concerned by the activity of the Nigerians in Eastern Europe, he said. "They are some of the most experienced heroin traffickers in the world," he said.

Mr. Green added that his agency had gathered intelligence that organized criminal groups from the former Soviet Union were using confederates in New York and Atlanta to smuggle drugs into the United States. Collapse of Controls

Drug syndicates are turning to Eastern Europe in the aftermath of the collapse of the Soviet Union, which has brought an end to rigid border controls, and in the wake of the war in Yugoslavia, which has led to a disruption of traditional drug routes. And the former Communist countries, confronted by a problem they did not face until recently, are woefully unprepared, handicapped by inadequate laws, a lack of experience and paltry resources.

For the drug dealer, once he has contraband in an Eastern Europe country, he finds it easier to move it West. This is because a person landing in New York or Amsterdam or London from Prague or Warsaw is not as likely to arouse suspicion as a person arriving from Bogota, Istanbul or Lagos.

This month, the German authorities seized 638 pounds of heroin entering the country from the Czech Republic in a shipment of Turkish nuts. Worth an estimated $18 million on the street, it was the largest heroin seizure ever in Germany, officials said. It was 200 pounds more than was seized in the record heroin seizure in New York in December.