The Soviets have sacked the head of their official trade union movement and replaced him with a man 14 years younger -- the latest sign of movement in Moscow's long immobile power pyramid.
A brief official announcement of the change March 5 also gave fresh evidence of the recently raised profile of a Kremlin figure considered one potential successor to President Leonid Brezhnev -- longtime Brezhnev aide Konstantin Chernenko.
With the official account offering no explanation for the trade union shift, interviews with diplomats and Soviet sources suggested various possibilities:
* The Poland catalyst. Since the worker upheaval next door, the Soviets have been paying more attention to their own, officially directed, union structure. No Soviet official is suggesting that unions here start acting like Solidarity. Yet as Alexandra Biryukova, a member of the unions' national leadership, told the Monitor last year, the Kremlin does feel ''we must know better the demands of workers, the moods and opinions of (the) broad masses.''
* The Suslov catalyst. Mikhail Suslov, the Politburo ideological authority who was that body's longest serving member, passed away in January. Some sources say the dismissed trade union chief was a Suslov protege, and maintain that the decision to remove him came barely a week after Mr. Suslov's passing.
* The corruption catalyst. A high-profile official campaign against corruption has been underway since last year. According to one non-Soviet communist source here, the trade union leader was dismissed in connection with corruption charges. This could not be immediately confirmed from other sources.
There seems little doubt, at least, that the dismissal of the union chief, Alexei Shibayev, amounted to a firing. The official Soviet news agency said the move had come ''in connection with his transfer to another job.'' Yet particularly since Mikhail Suslov's disappearance from the scene, foreign analysts have been discerning signs of possible creaks and strains at the top.
One development widely noted is the heightened profile of Politburo and Secretariat member Konstantin Chernenko. At the same time, an older colleague once considered by many diplomats the top candidate to succeed Mr. Brezhnev -- Andrei Kirilenko -- has withdrawn, or been nudged, into the shadows.
Kremlinologists are quick to caution against counting any figure out of a succession process whose details can be only guessed at. But the Chernenko-Kirilenko trend did seem to hold for the union shakeup. When the now-dismissed union chief was chosen in 1976, two members of the central Soviet leadership were reported present: Mr. Kirilenko and Ivan Kapitonov, a Secretariat figure specializing in party organizational matters. This time around, two senior men were also present: again, Mr. Kapitonov, but with Mr. Chernenko in Andrei Kirilenko's former spot.
The union reshuffle, meanwhile, has focused increased attention on reports from Soviet sources that the leader of the Communist Party youth wing -- Komsomol -- is likely to be replaced sometime this spring and transferred to the chair of the state committee for cinematography.
Although Komsomol leader Boris Pastukhov is not a member of the Politburo or Secretariat, he does quite frequently attend senior leadership meetings. He would be the most important figure within the party hierarchy to go since Premier Alexei Kosygin's resignation in late 1980.
The expectation is that a still younger man -- Pastukhov is 48 -- would get the top Komsomol spot. Yet if Mr. Pastukhov is shunted to the cinematography post, age would not seem the only reason for his loss of the Komsomol position. The film position carries considerable ideological importance in the Soviet order, but nowhere near the general influence that the Komsomol leadership does. (Mr. Pastukhov's predecessor in the Komsomol chair -- 49 years old when replaced -- was in effect promoted, taking over the Central Committee Secretariat's propaganda department.)
Despite Politburo member Chernenko's recently increased visibility, it remains unclear whether changes at the level of trade union leader -- or Komsomol chairman -- will prove contagious at higher levels.
Diplomats say one early indication could come at the next session of the party's full 467-member Central Committee. The date of that meeting -- formally slated to deal with food problems, yet with the power to announce leadership changes -- has yet to be made public. Yet diplomats say they have been told the committee could convene by the end of this month.