MIKHAIL GORBACHEV's Kremlin has gone beyond ``thinking the unthinkable.'' It is doing what had been unthinkable for most of Soviet history. Not only is the Kremlin acquiescing in anti-Soviet demonstrations in Baltic republics, permitting Polish leader Wojciech Jaruzelski to denounce Soviet actions against Poland in 1938-39, and authorizing plays, movies, and publications highly critical of the Soviet past. The Kremlin is even applying glasnost - openness - to the sphere of advanced military technology, reversing Russia's almost paranoid attitude toward security in decades and centuries past. Moscow's new openness in military affairs could facilitate arms control accords useful to both East and West. The changes are startling. Gone is the old motto, ``Disarmament first, inspection later.'' Instead, Soviet diplomacy has taken the lead in exploring new modes of verification to make arms control credible. First, Soviet authorities have permitted US seismologists to set up machinery on Soviet soil to record and measure underground explosions; initial experiments with dynamite give promise of more accurate identification of nuclear blasts than has been possible from outside Soviet territory. Second, Moscow has agreed to on-site inspection to police the proposed ban on intermediate-range missiles - leading Washington to back away from the most stringent measures it once championed, perhaps because US factories do not want Soviet inspectors. Third, and even more surprising, Soviet authorities have permitted US congressmen and their staff experts to tour the very installation that Washington charges represents the clearest Soviet violation of the 1972 Antiballistic Missile Treaty. THIS installation, just north of Krasnoyarsk, may well violate the treaty's stricture against ``early warning of strategic ballistic missile attack except at locations along the periphery of its national territory and oriented outward.'' The Krasnoyarsk site is far inland - the closest border is with Mongolia, more than 500 miles distant. The 1972 treaty also permits radars for ``purposes of tracking objects in outer space,'' but the Soviets now concede that Krasnoyarsk is poorly oriented for tracking satellites.
Not only has a congressional delegation walked through the radar, it has also been permitted to take photos inside and outside the structure.
Why was Krasnoyarsk built? And why have Americans been allowed to visit it? A recent study by the Union of Concerned Scientists argues that Krasnoyarsk, if completed, would fill an important gap in the early-warning system for the USSR, giving notice of missiles fired by US submarines in the northern Pacific. The Kremlin seems to have tried earlier to plug this gap by erecting two radars close to its borders, as permitted by the treaty, only to give up the effort because construction on Siberian permafrost proved too difficult. Krasnoyarsk, far inland - on firm soil and close to a railroad - would fill the gap. Even though it's a violation of the treaty, the Kremlin perhaps hoped to finesse this problem in the Soviet-US Standing Consultative Commission in the manner of other contentious actions by both countries under the ABM and Strategic Arms Limitation Talks (SALT) accords. In permitting on-site observation of Krasnoyarsk, the Soviets seek to demonstrate that there has been no serious breach of the ABM Treaty, no significant addition to the USSR's capacity to thwart a US missile attack. They may even want to show that Mr. Gorbachev's ``new thinking'' allows for admitting mistakes.
What then to do about Krasnoyarsk? Probably the White House would prefer that Moscow admit its error and close down Krasnoyarsk, while permitting the US to continue its own radar improvements. But this may not be realistic, for the Kremlin has its own complaints about US compliance with arms treaties. In 1975, Moscow charged that a radar the US was building in the Aleutians had been tested as part of an ABM system. Washington countered that the radar's function was to monitor Soviet missile tests - a purpose permitted by the ABM treaty. The Kremlin has also charged that the ``PAVE PAWS'' radars erected in many locations around the US ``can serve as a basis for providing radar backing for the ABM defense'' of the entire US territory. But Washington replies that these radars are oriented outward and are close to the US periphery, as required by the treaty.
Moscow's most serious charge is that the US has been upgrading radars in Greenland and England so that they can fulfill ABM roles well beyond their capacity when the 1972 treaty was signed. For two years now the Kremlin has been offering to stop work on Krasnoyarsk if the US halts what it calls ``modernization'' of its two overseas radars.
``If we were building the Krasnoyarsk radar in violation of the ABM treaty,'' Soviet Foreign Minister Eduard Shevardnadze said last week in Washington, ``we would not have invited US congressmen, US experts, to see that radar.... I really hope now that the US will reciprocate, and that our people will be able to see the controversial radar in Greenland....''
Perhaps we have the basis here for a compromise. Some Western experts agree that upgrading the Greenland and United Kingdom radars is probably a violation of the 1972 treaty. (One of the new radars is being built several miles from the original; both are much more powerful than those they are replacing.)
Both sides could halt work to plug gaps in their early-warning networks, or they could agree to proceed with present plans even though they represent possible violations of the ABM Treaty. If work at Krasnoyarsk and the two US overseas radars were halted, both sides would have gaps in their early-warning systems, especially the USSR (since one of the US installations is nearly complete and both are improvements of existing facilities). A halt in construction would give Moscow and Washington time to reaffirm their support of the ABM pact and to clarify the distinctions between early-warning and more threatening battle-management radars.
The other approach would be to permit both sides to perfect their early-warning systems, making allowances for geographical peculiarities not adequately considered in 1972, such as Siberian permafrost. Perhaps some form of on-site inspection could be introduced to ensure that neither side converted its early-warning radar into battle-management systems. SURELY the three contested radars are small change in the overall question of whether the superpowers continue to abide by the 1972 ABM Treaty. Can an accord be reached to limit ``strategic defense initiative'' experiments and deployments for a time period acceptable to both sides? If so, early-warning radars should present no major difficulty.
Regardless of how the Krasnoyarsk issue is resolved, the Kremlin's new openness demonstrates a political will to search out practical solutions to difficult problems. It also shows that Gorbachev is firmly enough in the saddle to impose radical departures from previous practice over the likely opposition of political and military conservatives. Now we shall see whether US diplomacy will match Soviet in creativity, candor, and the quest for compromise useful to both sides.