The momentum of Soviet military spending in the last several years has slowed to about half the rate sustained in the early 1970s, according to the outlines of a study by NATO experts.
The report is a short update of a more complete study by NATO and national experts last year. That report had already hinted at a possible slowdown in the Soviet Union's military buildup because of emerging economic and production difficulties. It estimated increases in Soviet arms spending of about 4 to 5 percent in the 1970-76 period and about half that rate from 1976 to 1982.
The new findings go against some official American and other pronouncements that still paint a portrait of a relentless Soviet arms drive. Nevertheless, they underline that Soviet military outlays between 1976 and 1982 ''continued at a very high level'' and that the Soviets could be on the verge of introducing a large number of new weapons programs.
Between 1976 and 1982, large quantities of equipment - including 75 major surface combat ships, about 2,500 intercontinental nuclear missiles and submarine-launched missiles, 6,000 tactical combat and interceptor aircraft, and about 15,000 tanks - have been delivered to the armed forces.
''There is evidence of large numbers of new programs at the research and development stage,'' the recent summary notes. It specifies that about as many systems are in the development stage at the beginning of this decade as there were at the beginning of the 1960s and '70s.
''It is projected that more systems will reach initial operational capability in the 1980s,'' it adds, ''than in either the 1960s or 1970s.''
Among the new Soviet weapons systems said to be approaching such a level of readiness are fighter,airborne warning, and control aircraft, ballistic and cruise missiles, space systems, and submarines.
The NATO report adds that defense production facilities have been expanded, which could imply a resumption of the rate of Soviet defense growth of the early 1970s.
The slowdown in recent years could have resulted from a general Soviet economic slump, supply bottlenecks, or difficulties in introducing advanced technologies, rather than a formal policy decision from the leadership.
The report also concludes that ''any major effort to accelerate sharply the level of military procurement could exacerbate Soviet economic problems and would pose particularly difficult choices of resource allocation.''