MOSCOW (AP) _ Soviet authorities have concluded an anti-narcotics operation codenamed ''Poppy 86'' that resulted in more than 4,000 arrests and the destruction of thousands of acres of illegal crops, Pravda reported today.

The Communist Party daily, as part of a campaign against illegal narcotics, published a long interview in which Interior Minister Alexander V. Vlasov answered questions from newspaper readers on the drug problem.

For decades, the Kremlin refused to acknowledge the existence of drug addiction in the Soviet Union, saying it was a phenomenon peculiar to capitalism.

But Vlasov, who oversees the uniformed police, said this long ''silence about the extreme danger of drug addiction blunted social vigilance, deflected the attention of the militia, medical profession, society, families and schools. Willingly or unwillingly, this eased its spread.''

Narcotics and addiction have been given greater attention in the official press under Soviet leader Mikhail S. Gorbachev, part of his policy of increased openness on selected social themes.

As a result, Vlasov said, law enforcement agencies launched a major campaign against drug production and trafficking.

Previous press reports have said Soviet drug users consume mainly products from poppies - such as opium and heroin - as well as hashish and various types of marijuana that grow wild or are cultivated in southern regions.

''The sowing areas and transportation routes are well known,'' Vlasov said. ''During the course of the recently completed operation 'Poppy 86' alone, more than 3,000 hectares (7,000 acres) of illegal crops (and) 100,000 hectares (240,000 acres) of wild marijuana were destroyed.''

About 300 drug traffickers and 4,000 people working in the production of narcotics were arrested, Vlasov said.

Vlasov said the number of drug addicts in the Soviet Union has grown significantly over the past five years and that 46,000 people are diagnosed as having an addiction.

He did not provide any estimate on how many other people might be using drugs without being officially registered as addicts. The scale of the operations busted in ''Poppy 86'' suggested that drug use is more widespread than Vlasov's figures indicate.

Eighty percent of all drug users in the Soviet Union are under 30, Vlasov said.