Several high-level East European sources, based on direct contacts with Moscow, reveal that:
* Mikhail Gorbachev, the ''young hopeful'' for the Soviet leadership after the death of Yuri Andropov earlier this month, did not lose out in a power struggle. He is already seen within the leadership itself as very much the man of the future.
* Konstantin Chernenko and three senior, equally veteran colleagues beneath him have themselves acknowledged that Chernenko's leadership is a transitional one. The Politburo, the Soviet Union's policy-making body, made a collective decision in favor of transitional leadership after it had thoroughly and outspokenly thrashed out the future.
* There is and will be no change in the collective-leadership concept. Continuity - that is, allowing Mr. Andropov's domestic policies to continue intact - remains the order of the day under the new leadership.
This inside view of events before and following Andropov's death comes from highly authoritative East European sources, based on talks that some East-bloc leaders had with Mr. Chernenko and some of his associates during their visit to Moscow for the funeral.
American Vice-President George Bush and British Prime Minister Margaret Thatcher have not disclosed any details publicly, but they may have drawn some similar impressions during their shorter encounters with the new Soviet leader.
The choice of Chernenko was determined well before Andropov's passing. It was quite clear to Andropov's Politburo colleagues long before he died that he probably did not have long to live - or that, at best, he could not continue to carry the burden of office.
The end, when it came, however, was ''somewhat sudden.''
One East European leader has since told a senior diplomatic visitor of his concern that so many Western observers had regarded the Chernenko choice as a ''step backward,'' i.e., to a more conservative approach.