Brussels — The Soviet economy will continue to ''muddle through'' in the years ahead, holding its own but falling far short of Kremlin expectations, according to experts attending a NATO-sponsored symposium here last week.
''There is no evidence that the slowdown in Soviet growth will be reversed,'' said Jiri Slama of the Osteuropa-Institut in Munich.
The experts - from government, academia, and business - offered reasons for their gloomy forecasts. These ranged from the expected depletion of readily available raw materials to the Soviet Union's ''inelastic'' political bureaucracy.
But their conclusion was the same: The Soviet leadership will be faced with an agonizing choice between bolstering the civilian economy and expanding the ever-growing military machine for some time to come.
''Growth increments are not expected to be sufficiently large to permit the leadership the luxury of serving adequately the needs of the military and civilian sectors simultaneously,'' Byron Doenges of the United States Arms Control and Disarmament Agency told the symposium.
''Increasing competition between the two sectors for scarce quality resources will agitate the leadership for the remainder of the decade and, perhaps, the century,'' he said.
Despite improvements in the Soviet economy last year, the average annual growth rate for the rest of the decade is expected to be no more than 2 percent, while spending on defense is expected to be at least twice that, according to experts.
Soviet military procurement, in fact, has leveled off since 1976. But the US military buildup under the Reagan administration has put pressure on the Soviets to return to a growth rate in the defense sector of 4.5 or more, says Doenges. This was a goal set for the next three years by Defense Minister Dmitri F. Ustinov in a Pravda article last November.
Luigi Marcolungo of the University of Padova in Italy underscored the ''very tense political situation and jeopardized economy'' which Yuri Andropov inherited from Leonid Brezhnev.
Clearly, Mr. Andropov's short-term impact on the Soviet economy - which resulted, for example, in greater labor discipline - was positive. But he made no major structural changes in the overall functioning of the economy, and the ''Andropov effect'' can't be expected to last for long, Mr. Marcolungo said.
Some of the Soviet problem can be traced to factors beyond the Kremlin's control. The changing demographic picture, for example, is leading to a steadily decreasing work force.
But there are steps the new Soviet leadership under Konstantin U. Chernenko could take, the experts meeting here agreed. Few doubted, however, that Chernenko will be a man of action.
''Problems in generating, assimilating, and diffusing new technologies have constantly plagued the Soviet economy,'' according to John A. Martens of the US Commerce Department.
''If no significant improvement occurs, the Soviet Union will face an economic drag from the coming decline in the growth of its industrial labor force and will be frustrated in its ability to compete with the West.''
Joseph S. Berliner of Brandeis University tried to explain why the Soviets have failed in their 20-year effort to accelerate technological progress. He cited a statement made by Mr. Andropov last June: ''The manager who takes a single 'risk' and introduces new technology in his enterprise often loses out, while the one who avoids innovation loses nothing.''
Western evaluations of Soviet postwar innovations have been ''largely negative,'' according to Mr. Martens, ''and Soviet industry has even had considerable difficulty in utilizing much of the technology it purchased from the West.''
Most experts expect Chernenko to repeat the ''lessons'' of the early 1980s, allocating resources to the military at a faster rate than that of the civilian sector.
''This is bound to result in serious complications for the Soviet leadership, '' Byron Doenges predicted.
The current watchword in the Soviet Union is ''caution,'' Mr. Marcolungo says. He adds that although ''experiments'' abound, there is no major economic reform in the works.
''But if in the near future the improvements registered last year are not consolidated through structural adjustments in capital productivity and overall efficiency,'' he says, ''there could be a further worsening in the general equilibrium of the Soviet economy.''