Moscow — The evidence is inescapable: The transition from Leonid Brezhnev's command of the Soviet policy machine has begun in earnest. And it has entered a delicate phase with two powerful, yet strikingly different, personalities sharing center stage.
A Soviet source June 29 denied reports from some diplomats here that Mr. Brezhnev's health had taken a turn for the worse. Yet the Soviet leadership has recently effected a reshuffle, transferring the bulk of day-to-day power to a pair of Mr. Brezhnev's Politburo colleagues.
One is Yuri Andropov, who has ceded his 15-year command of the KGB security police and rejoined the Communist Party's central Secretariat in the powerful position of chief specialist on ideology and foreign affairs.
The other is long-time Brezhnev aide Konstantin Chernenko, who, in four years as a full member of both Politburo and Secretariat, has become much more than that.
Soviet officials who have attended recent Secretariat sessions or been briefed on them told the Monitor that Andropov and Chernenko are currently ''sharing'' the chairmanship of that body. The Secretariat makes a wide range of day-to-day Soviet policy decisions and ''frames'' others passed up to the Politburo.
Mr. Brezhnev, formal chief of the Secretariat, very seldom attends its meetings. For many years, the effective chairman was Kremlin ideological and foreign policy authority Mikhail Suslov. But Mr. Suslov passed on in January. His departure served as a major catalyst for the recent reshuffle.
Monitor interviews with five senior Soviet officials left little doubt that a sense that transition at the top might be approaching was another spur for action.
On the heels of Mr. Suslov's passing, it was Mr. Chernenko, the stocky, white-haired Brezhnev protege, who became de facto chairman of the Secretariat. Soviet officials said he was also deeded a good part of Mr. Suslov's territory in issues of ideology and foreign policy within that body.
Then, there was some tugging and jostling within the Soviet leadership as a longer-term allotment of Mr. Suslov's responsibilities and prerogatives was worked out. ''Some personal differences,'' is what one senior official called the process. He said that Western Kremlinologists overstated its intensity.
Finally, at the end of May came Yuri Andropov's switch from the KGB to the Secretariat. Crucial to the eventual transition picture is what comes next.
An official who knows both Messrs. Chernenko and Andropov said he hoped and expected the two would work together as a team. Referring to the current balance , he said: ''There is already a setup where things can be collectively run.'' This was one reason plans were going ahead for President Brezhnev to leave ''soon'' for vacation in the south, earlier than in past years.
The official said the current Chernenko-Andropov duet was a stabilizing factor. He did not share Western analysts' concern over ''personal aspects'' of the transition process.
Other officials interviewed, while not predicting friction between the two current Secretariat acting chairmen, said the precise nature of their collaboration was still ''being worked out.''
How this is resolved will likely determine which, if either, of the two men becomes party general secretary when Mr. Brezhnev is gone - or whether another candidate will get the nod. Soviet history suggests that one complicating factor is the political system's tendency to abhor truly collective rule in preference for one dominant figure.
Senior officials, meanwhile, raise a more immediate and practical problem: the power vacuum left by Mr. Suslov, who wielded enormous personal influence.
The current picture is this: Andropov, the officials said, has in effect been handed Suslov's portfolio for ''ideology and foreign policy.'' But Chernenko retains a degree of input in both areas, and the overall Secretariat power vacuum left by Suslov is being filled partly by each of the two other men.
If foreign Kremlinologists like to remark on Chernenko's lack of a ''power base'' beyond Leonid Brezhnev, within the key transition constituency of senior party officials that base is a lot bigger than it looks.
Described by associates as a ''determined,'' if not brilliant, man who organizes well and surrounds himself with able lieutenants, Chernenko has headed the Secretariat's ''general department'' since 1965. Joining the Secretariat itself 11 years later, he retained that territory and thus, officials say, has been responsible for funneling commissioned reports on all policy issues to the Secretariat and Politburo.
In this role he has exercised enormous influence within the Soviet leadership. He has also ''absorbed'' considerable foreign policy experience alongside Mr. Brezhnev, and via ''the 20 to 30 percent, or whatever, of Politburo work dealing with foreign policy.''
Andropov has learned foreign policy, particularly as it relates to the East bloc, first hand. He was ambassador to Hungary when Soviet troops marched in 26 years ago. Afterward he served on the Secretariat as a specialist dealing with East-bloc parties.
In this capacity, he also was in charge of a more general foreign policy advisers' group headed first by Fedor Burlatsky, then by US-affairs specialist Georgi Arbatov, both proponents of efforts to improve relations with the West. Andropov himself has never officially visited the West.
Although described by associates as tough -- a label that can be assumed for a man who headed the KGB for 15 years -- Andropov is portrayed as more than a mere secret policeman. Officials say he initially resisted taking the military rank that went with the KGB leadership. He is said to have a wry sense of humor, even to have tried his hand at an occasional comic verse, and to have taken private lessons in English, although he attained nothing near fluency.
Officials say he seems to lack Chernenko's single-minded interest in political matters, and he enjoys reading Russian, and occasionally Western, literature.