Yuri Andropov's assumption of the ceremonial Soviet presidency in addition to the leadership of the Communist Party may signal insecurity more than strength. The move in the Soviet parliament Thursday did leave him without a visible rival personality among the top leadership - and in this sense it was a consolidation of position. But the promotion Wednesday of Leningrad party chief Grigory Romanov to a key Moscow post could make him worth watching in the longer run.
Mr. Andropov already had the real seat of Soviet power, however: the leadership of the Communist Party, with automatic status as commander in chief, in which he succeeded Leonid Brezhnev last November.
His key pre-transition rival - Politburo member Konstantin Chernenko, a close Brezhnev protege - fawningly nominated Mr. Andropov for the presidency. Last year Mr. Chernenko, in notably more guarded tones, had nominated him as party chief.
At a meeting of the party Central Committee Tuesday and Wednesday, Mr. Chernenko had already shifted to his more agreeable line, giving what amounted to a ''unity'' speech lining up firmly behind Mr. Andropov.
The main import of the committee session, and of the Andropov-Chernenko duet on the presidency a day later, may lie in the Soviet leader's perceived need to convey a sense of unchallenged command to the nation's party and government bureaucracies.
Senior officials who have proven reliable in the past say Mr. Andropov felt neither need, nor desire, for the largely decorative presidency in his first months as party leader.
Indeed, they have painted him as leery of a Brezhnevian fondness for the titles and trappings of power, and as feeling that frillish duties may hinder more than they help real policy work.
Mr. Brezhnev, assuming the presidency in 1977 after 13 years as party leader, became the first Soviet leader to hold both posts together - and in so doing ousted veteran colleague Nikolai Podgorny.
A ranking official, saying ahead of time in a Monitor interview that Mr. Andropov would not become president at a parliament session last November, added: ''I personally would not advocate Andropov's becoming president. . . . We have a Constitution and, under it, a (separate) party general secretary and a president.''
Another senior source said later that Mr. Andropov would ''definitely'' not become president at a December 1982 session of parliament, either. ''My hunch is he will not do so at all,'' he said, adding: ''It can be said now that Brezhnev did it partly to get rid of someone. . . .''
Andropov's reported reluctance to take on the presidency seems especially relevant, given diplomats' reports that, although he is mentally sharp, he is physically ailing. Reliable information on this subject is impossible to get here. But Andropov did surprise diplomats Thursday by delivering his acceptance speech as president sitting down.
One reason Brezhnev assumed the presidency - possibly a factor in Andropov's move - is that protocol pairs foreign heads of state with presidents and not party chiefs. Also, as a rule, it is presidents who formally sign treaties.
Yet in Andropov's seven months as party leader, this hasn't been a visible problem. Leaving duties like airport welcomes to Vice-President Vasily Kuznetsov , he has fulfilled more meaty ''presidential'' functions. This is certainly far truer of him than of Brezhnev during his first five or six years in power.
When Finnish President Mauno Koivisto visited Moscow, Andropov held the major talks with him. And Andropov gave the policy speech at a banquet for the head of state.
Whatever tugging may or may not have been going on in private, the Kremlin has publicly spoken with one voice on major policy issues: Andropov's.
In a speech at the Central Committee session Wednesday, Andropov himself seemed to sense potential bureaucratic grumbling over extending Brezhnev's blurring of boundaries between party and state.
Although he did not refer explicitly to the top posts, he offered what, in retrospect, may have been an attempt to reassure critics: ''It is very important to reassure the correct distribution of functions between the party and state.''
Senior officials were not immediately available for comment on Andropov's selection as president. But past remarks suggest that the party chief and his senior Kremlin colleagues may have been unable to agree on a compromise alternative.
Post-transition comments to foreign diplomats here indicated that at least two men, Mr. Chernenko and Foreign Minister Andrei Gromyko, had been offered the presidency soon after Andropov succeeded Brezhnev as party chief, but that neither wanted it.
Andropov may also have decided that, whether he wanted the presidency or not, it was better to take it than risk giving it to a potential rival, or to leave the post open any longer.
This approach would jibe with the tone of the Central Committee meeting Tuesday and Wednesday, which grouped some 450 members of the nation's political elite. The Andropov presidency, and the Andropov-Chernenko show of unity at the committee session, both seemed to be intended to convey a sense that ''transition'' at the top is over.
The message was that Yuri Andropov is running a coherent, tranquil team, and that the nation's bureaucracy should now busy itself with ''discipline'' and economic efficiency, watchwords of Andropov's early months in power.
It is conceivable, meanwhile, that the two-day session of parliament could announce further government personnel shifts. But none had been announced at time of writing.