Moscow — In the first days of the Soviet Union's post-Brezhnev era, the early watchword in official statements is ''continuity.''
But there are now built into the 65-year-old Soviet system pressures both for and against long term change. Which will prevail will only become clearer as the new era unfolds.
With virtually no outward effect on Moscow's ordinary bustle, the leadership announced early Nov. 11 that Leonid Ilyich Brezhnev, Soviet Communist Party chief for the past 18 years, had passed on some 24 hours earlier.
Mr. Brezhnev's tenure, which overlapped five American presidencies, has deeded both achievements and unresolved problems that will do much to define the initial policies of his successors, whoever they turn out to be. No major shifts in domestic or foreign policy are expected in the immediate future.
As for relations with the United States, the Kremlin in effect served notice in a statement Nov. 11 it is determined not to play the role of supplicant in any early thaw following Mr. Brezhnev's passing.
The first, necessarily inconclusive, sign was that the new party leader will be Yuri Andropov, a man until recently in charge of the KGB security organization but portrayed by Soviet colleagues as more than a mere secret policeman. Mr. Andropov was named to head the commission organizing Mr. Brezhnev's funeral Nov. 15 - a task that fell to then incoming leader Nikita Khrushchev after the death of Joseph Stalin in 1953.
But the decision on a new party leader must be made, or at least ratified, at a meeting of the full Communist Party Central Committee. At time of writing, there had been no announcement of such a session, although one has long been scheduled for Nov. 15.
Under heavily centralized Soviet rule, it is inevitable that the individual or individuals inheriting Mr. Brezhnev's power will leave a particular stamp on future policy.
But various aspects of Mr. Brezhnev's complex legacy will also matter greatly:
* The departed Soviet party leader built his nation into a genuine military superpower on the order of the United States. Maintaining officially proclaimed ''parity'' with US weaponry is sure to be a policy priority of the new leadership.
* Mr. Brezhnev also pursued closer relations with the West. Economically, these centered on Western Europe. He also began a process of nuclear arms-control negotiation with the Americans. One effect has been to make the Soviets' daunting task of funding both guns and butter at least marginally more manageable. Thus, this Soviet vision of ''detente'' is not likely to be abandoned rashly by the men who follow Brezhnev.
* Brezhnev also oversaw a considerable ''professionalization'' of the Soviet decisionmaking process, involving in it many more people, often more-specialized people. Many of these are likely to stay in place at least for the time being. Having worked not only with Mr. Brezhnev but also with other members of the leadership, they are likely to contribute to a sense of continuity in Soviet policy at least until a new ruling team gets firmly in place.
But Leonid Brezhnev also deeded pressures for change:
* Soviet moves to consolidate or expand influence in the third world, portrayed as part of an ideological competition with ''Western imperialism'' that could and should survive East-West detente, came to involve a significant drain on Moscow's resources. Soviet relations with Cuba and Vietnam are two examples. In Afghanistan, Moscow's involvement includes not just money but men.
* Although helping millions of Soviet citizens to get better clothing and better housing, Brezhnev unsurprisingly failed to rewrite the equation of guns vs. butter in a way allowing both military superpowerdom and the kinds of consumer goods the country has come to crave. Particularly in Mr. Brezhnev's later years, in part due to an unwelcome assist from the weather, the country's chronically weak agricultural sector faltered, and widespread food shortages resulted.
* In an inevitable spinoff of Brezhnev-era detente with the noncommunist world, large numbers of quite ordinary Soviets acquired a greater exposure to things non-Soviet. On the one hand, this has resulted in a ''consumerism,'' where blue jeans and Beatle songs compete for Soviet attention with the ideological business of Leninism. It has also been a factor in producing a greater awareness of life, if not necessarily ideology, outside Soviet frontiers.
All this suggests no neat formula for predicting what the post- Brezhnev era will bring.
But it implies that the new regime's policies will be born of contradictory forces for ''continuity'' and change. Soviet history, meanwhile, implies that the few men at the very top of the post- Brezhnev hierarchy will spend the immediate future in a jockeying for position that will ultimately produce at least some measure of departure from the policy of ''continuity'' now proclaimed.