THE Soviet Union's nuclear stockpile is significantly larger than that of the United States, consisting of 33,000 warheads, bombs, shells, and mines, according to an authoritative new study. This arsenal is carried on some 60 delivery systems, ranging from the 35-year-old SA-1 Guild surface-to-air missile to the new SS-24 mobile intercontinental ballistic missile (ICBM). It is split roughly half-and-half between strategic weapons and shorter-range tactical nukes, the report by the Natural Resources Defense Council (NRDC) estimates.
The policies of Soviet leader Mikhail Gorbachev have not yet led to large-scale reductions in the Soviet nuclear stockpile. But the NRDC report points out that total explosive yield, in megatons, of Soviet nuclear weapons peaked in the mid-1970s and has been declining ever since, perhaps by as much as one-third from its historic high.
Total explosive yield of the US stockpile has similarly been steadily falling since it peaked in the 1960s. The total number of US nuclear weapons is a closely guarded secret, but rough estimates by private analysts put the figure at 25,000 to 28,000.
The NRDC's Soviet Nuclear Weapon report is part of a comprehensive nuclear data base that the organization has been compiling throughout the 1980s. It relies largely on Pentagon reports obtained through Freedom of Information Act requests.
It concludes that Soviet nuclear forces are kept at a much lower level of peacetime alert than are US counterparts. Only 50 to 60 percent of Soviet land-based ICBMs are ready to fire at any given time. No more than 15 Soviet missile-carrying submarines, about 20 percent of its force, is at sea on a given day.
While many Soviet fighter and fighter-bomber jets can carry nuclear bombs, there is a shortage of corresponding pilots trained and certified for nuclear missions, according to the NRDC study's authors. Few Soviet fighter bases have nuclear-weapons storage facilities.
Of the 33,000 total Soviet nuclear weapons, about 7,600 are warheads for land-based ICBMs, which Soviet doctrine has long held to be the preeminent offensive nuclear force. About half of these are warheads for the SS-18, the heavy 10-warhead behemoth that the Pentagon considers the most threatening of Soviet weapon.
Some 4,000 Soviet warheads are for sea-launched ballistic missiles (SLBMs). The Soviet SLBM force is currently carried on 64 subs, with four to six more under construction.
Aircraft-carried weapons account for about 7,400 weapons in the Soviet nuclear stockpile. The bulk of these are gravity bombs, though Soviet nuclear air-launch cruise missiles have increased in recent years to 2,200.
The NRDC authors classify 4,000 Soviet warheads as ``strategic defensive.'' These include warheads mounted on Galosh and Gazelle antiballistic missiles deployed around Moscow, and surface-to-air missiles designed to clear intruding aircraft out of Soviet skies.
The Soviet armed forces received their first nuclear weapons in 1953 or '54, after a crash building program launched by Stalin the day after the US bombed Hiroshima. By 1969 the USSR had caught up to the US in numbers of ICBMs. The Soviets began mounting multiple independently targeted reentry vehicles (MIRVs) on both land- and sea-based missiles in the early 1970s. By 1977, the Soviets had more total ICBM warheads than did the US.
Among other new weapons, the Soviet military is developing a follow-on to the SS-18. The NRDC report predicts the USSR ballistic-missile submarine force will shrink in size over the next 10 years, as subs from the Yankee, Delta, and other older classes are retired.