MOSCOW -- By the convoluted standards of Soviet foreign trade, Boris I. Korobochkin's barter deal seemed simple enough.
The Singapore company would get 50,000 tons of Soviet-manufactured mineral additives for livestock feed. In trade, it would supply the Soviet side with 1,200 personal computer systems, plus a number of photocopiers, telefax machines and other equipment in short supply.
However, to Mr. Korobochkin, the would-be middleman, the deal brought not the intended profit but a score of KGB interrogations, nine volumes of evidence and a month in Moscow's infamous Lefortovo prison.
What appeared to the naive outsider as a normal commercial transaction appeared to the KGB as a crime. "Contraband," they called it, and they put a team of investigators on the case for most of last year.
Mr. Korobochkin, an unflashy, gray-suited, chain-smoking, 58-year-old workaholic, said he was shocked when the KGB came to the hospital where he was undergoing a cardiac examination to arrest him Oct. 4.
But he said he was even more surprised when, at the conclusion of his trial a few weeks later, he was acquitted.
"Before, I didn't think the KGB could just come and take me away. Now, I think they can do whatever they like," Mr. Korobochkin said in his Moscow office, to which he returned directly from the courtroom where he was set free.
"But strange as it seems, now I'm more convinced than before that positive changes are taking place in this country and that we'll probably end up with a law-governed state," he said. "I thought I'd get the maximum, 10 years. With a KGB case like this, in the past, you could never have gotten an acquittal. Never."
The case dramatizes the hazards faced by neophyte Soviet businessmen testing the waters of private commerce for the first time in seven decades.
It also raises questions about the position of the KGB, to which President Mikhail S. Gorbachev is giving a larger and larger role in fighting "sabotage" and "speculation" in the ruins of the Soviet economy.
The Korobochkin case and others like it suggest that the KGB might have an additional goal: strangling the new private sector to protect the economic monopoly of its traditional master, the state-Communist Party bureaucracy.
Despite spending October in prison as "an especially dangerous state criminal," Mr. Korobochkin does not rush to place all of the blame on the KGB.
"I don't think it was the KGB's case. I think it was the case of other forces," he said, indicating that he had in mind the Communist Party and the state ministerial bureaucracy. "I think the KGB was simply the instrument."
For its part, the KGB denies that it got orders from above but won't say how the case started. "Let's just say, 'Information was received,' " said Moscow KGB spokesman Sergei P. Bogdanov.
Mr. Korobochkin, a mathematics graduate of Leningrad State University, had the resume of a distinguished Soviet technocrat.
He had taught at Latvian State University, applying mathematical theory to practical problem-solving. He had held high-level technical jobs for Aeroflot, the Soviet airline, and for Gosplan, the state economic-planning agency.
But in February 1989, itching to try his hand at newly legalized entrepreneurship, he quit his state job and opened a cooperative called Informsystem, essentially a private business. Early this year, he reorganized his business into an association of state and private enterprises called Conversion.
The Singapore deal was organized by Informsystem. A colleague put him in touch with Maitrad Computer Systems, a Singapore business that had expressed interest in acquiring tricalciphosphate feed additives.
Mr. Korobochkin says, and the KGB has not denied, that the state producer of the mineral supplements, the Khimprom plant in the Ukrainian town of Sumy, was having trouble selling them inside the Soviet Union. So Informsystem organized the deal -- pure barter, like many Soviet export contracts, because of the non-convertibility of the Soviet ruble.
One-third of the computers received in trade were to go to the data center of the Soviet Ministry of Railroads, which desperately needs themto untangle its notoriously tangled freight yards. The rest were to be divided between Khimprom, Informsystem and the local government in Moscow's Sokolniki District, where Mr. Korobochkin's firm is situated.
But late in 1989, Soviet customs officers froze the shipments, and the KGB summoned Mr. Korobochkin for questioning. His troubles coincided with a national campaign to discredit cooperatives that led to a shouting match in the Soviet parliament and fueled the rise to fame of Ivan K. Polozkov, a reactionary politician who later became chairman of the Russian TTC Communist Party.
In more than 20 interrogations, each lasting at least six hoursKGB agents found errors in the paperwork related to the deal, Mr. Korobochkin said.