Washington and Moscow get set to deal. Despite distrust, nations edge into serious arms negotiations

At the 11th hour, despite their mutual distrust, Washington and Moscow are finally edging into serious arms control negotiations. The exchange of the past few days -- with presentation at the Geneva talks of the new United States proposal on offensive strategic and intermediate-range nuclear weapons and delivery of Soviet leader Mikhail Gorbachev's letter to President Reagan -- suggest that:

The global numbers of the two sides are surprisingly close, though the specifics of the subcategories remain far apart.

Any agreement that emerges -- despite all the rhetoric of the past five years about ``deep cuts'' -- is likely to have much in common with the more modest pattern of the first and second Strategic Arms Limitation Treaties (SALT I and II) in capping rather than reversing the arms race.

Such modest nuclear ceilings could still greatly enhance international stability and prevention of war.

The political decision actually to risk a broad arms control agreement -- including on the US side willingness to restrain ``star wars'' -- has not yet been made in either capital, and would be the last piece to fall (or not to fall) into place.

Thus, the proposed limits on strategic nuclear warheads are 8,000 (Soviet offer of last June) and 7,500 (latest American offer, according to leaks in Washington). This would represent cuts of about 30 percent from present arsenals of 10,000 or 11,000 each.

Within the 7,500 to 8,000 ceilings, the big sticklers for Washington are Soviet demands for restrictive limits on bombers and strategic cruise missiles -- the US is now deploying the latter, in advance of the Soviets -- and Soviet permissiveness in land-based ballistic missiles and in the ``heavy'' missiles that Moscow has a monopoly on.

Within the 7,500 to 8,000 ceilings, the big sticklers for Moscow are the obverse American permissiveness in bombers and cruise missiles and restrictive limits on land-based intercontinental ballistic missiles (ICBMs) and especially on ``heavy'' ICBMs.

According to the Washington leaks, the US proposal would require 50 percent-plus cuts in both Soviet subcategories, down to 3,300 for all land-based missiles and 1,650 for heavy or mobile ballistic missiles. Currently the Soviet Union puts almost three-quarters -- the US only one-quarter -- of its strategic warheads on land-based missiles. The Soviet Union has 308 heavy 10-warhead SS-18s and is deploying a mobile land-based missile in advance of the US.

In addition, the US demands that the total strategic ``throwweight,'' or payload, on ballistic missiles come down to 3,000 tons; Soviet throwweight is 6,000 tons at present, while American throwweight -- following rapid reductions in the 1970s as technological improvements made warheads smaller and more accurate -- is only 2,200.

The new goal of 30 percent cuts in strategic warheads is more realistic, the old goal of 50 percent more utopian. The Soviet fallback in June from 50 percent to 30 percent was in fact a major signal to US analysts that Moscow might now be negotiating in earnest. The powerful Soviet military would never accept anything so radical as 50 percent cuts, the reasoning went, in the only instrument that makes the Soviet Union a superpower: military might. It might, however, accept 30 percent, if the mix was right and reassured the Soviets in technological or other areas of military concern.

If agreed on, 30 percent reductions would, for the first time in nuclear arms control, cut ballistic missile warheads rather than just block their expansion. This would hardly diminish today's overall nuclear arsenals, of course, since air- and sea-launched cruise missiles of sub-strategic range will shortly be expanding. And even in ballistic missile warheads alone -- given the rapid increase in arsenals in the 1980s -- ceilings of 8,000 would bring the US back only to its 1979 level (the year the unratified SALT II treaty was signed) and would allow Moscow an expansion of 50 percent-plus over its 1979 levels.

Nonetheless, any agreement today on 30 percent reductions would be highly significant in constraining the kinds of warheads that are most ``destabilizing'' and dangerous: those with a potential capacity to launch a ``first strike'' to neutralize the enemy's own retaliatory nuclear forces. Ever since the nuclear age began, the peculiar destructiveness of nuclear weapons has meant that deterrence, or the prevention of outbreak of nuclear war, has rested on both sides' ability to retaliate and turn any enemy attack into a mutually suicidal affair; a first-strike capability would undermine confidence in this standoff.

Thus, presidential candidate Reagan's concern about a ``window of vulnerability'' in the 1980 election campaign was aroused by a perceived Soviet ability to break out of the stalemate by using Soviet heavy missiles to cancel American deterrent power in some surprise attack that could wipe out disproportionate numbers of US missiles. Soviet concern about President Reagan's research program into space-based defense, the Strategic Defense Initiative (SDI, or ``star wars''), is based on a reciprocal fear that the US could eventually do the same to the Soviet Union by using even a leaky SDI to foil Soviet retaliation and therefore Soviet deterrence.

The latest US offer in Geneva deliberately postpones the final knock-down fight over any SDI trade-off within the Reagan administration.

What administration moderates who favor arms control now seem to be gambling on, however, is the hope that a near deal on reducing offensive first-strike weapons would establish a momentum to compel final agreement. If everything were in the bag except for mutual restraints on strategic defense, they could then hope to convince Reagan that he had a historic opportunity: that SDI would accomplish its goal of defense much more cheaply by serving as a bargaining chip today to thwart buildup of Soviet first-strike capability than by being deployed as a war-fighting weapon tomorrow against vastly proliferated Soviet warheads. Concurrently, they would hope that moderates in Moscow would persuade Mr. Gorbachev to prefer today's imperfect deal to tomorrow's open-ended arms race.

Both sides agree that if any deal is going to be struck within the next decade, it probably has to be struck in the next few months, before the US presidential campaign heats up. Hence the urgency of the just-opened round of Geneva negotiations and superpower maneuvering toward a second summit.