PRESIDENT Reagan recently announced his intention to modify US adherence to the SALT II treaty of 1979 unless the Soviet Union begins to comply fully with the pact. According to the Reagan administration, the Soviet Union has violated SALT II by both encoding missile telemetry and testing a second new light ICBM -- the SS-X-25. The President's new policy will enable the United States to make ``proportionate responses'' to such breaches of the treaty unless they are soon corrected. In response to Soviet tests of the SS-X-25, for example, the administration hints that the US will speed up development of its second new light missile -- the mobile Midgetman. The President deserves credit for not abandoning SALT II in order to penalize the Soviet Union. But to set the stage for taking unilateral steps to alter the terms of adherence to SALT is counterproductive. At this delicate juncture in US-Soviet relations, the policy risks countermeasures by the Kremlin and a de facto end to the treaty regime. Pressures will build in both Washington and Moscow to deploy new nuclear weapons in excess of the treaty's limits; such pressure could reach the boiling point when the treaty is due to expire this December.
Reagan's threats of unilateral action also defeat the purpose of the arms control negotiations in Geneva, which are meant to build mutual trust in order to reduce the growing risk of nuclear conflict. Until the President has a new treaty to replace SALT II, he should try to maintain the accord intact, not seek acceptable ways to undercut it.
President Reagan should seriously consider whether it would be easier to extend mutual compliance with SALT II by working with the Soviets rather than against them. Both superpowers have a vital stake; they should use diplomacy to establish an interim framework for upholding the treaty until it is replaced by a new agreement.
The Soviets will remain reluctant to address US concern over SALT II compliance unless the Reagan administration makes a more formal commitment to it. In the President's view, he has ``gone the extra mile'' by giving the Soviets another opportunity to correct their past record of compliance. He should now take a further step and offer to join Secretary Mikhail Gorbachev in a declaration formally committing both nations to abide by SALT II. In exchange, the Soviets would be required to own up to questionable compliance practices and to take remedial actions. Such a step has a historical precedent; the superpowers made a joint commitment to uphold SALT I when it was due to expire in 1977.
As part of the declaration, the leaders could resolve one of the critical compliance issues by agreeing to permit the testing and deployment of a second new light ICBM. The SALT provision prohibiting the new missile is outdated for both the Soviet Union and the US, which is scheduled to begin testing the Midgetman in 1987. In the joint statement, the President could condition US adherence to SALT II upon both equal Soviet restraint and progress toward a new arms control treaty, thereby leaving his options open to reverse the policy and keeping pressure on the Kremlin. The Soviets are determined to consolidate the gains of d'etente and salvage SALT II; this should give the US ample leverage to secure a satisfactory commitment to renewing the accord.
Retaining SALT II intact would be more conducive to arms reduction than breaching it one step at a time. Absent firm SALT limits, both nations will be tempted to accelerate various strategic initiatives to gain leverage and to protect against the other's new advantages. Many more-accurate and powerful nuclear weapons might be deployed, making the goal of major reductions even more illusive. It would be harder to reach the President's aim of a ceiling of 5,000 warheads from a level of 15,000 than 10,000.
Retaining the SALT II ceiling and subceiling on missiles and bombers would provide a base line for future reductions. Without this base line, the US delegation in Geneva would waste time negotiating over what categories of weapons to reduce instead of how many.
A joint US-Soviet declaration on SALT II, by preserving a stable negotiating setting in Geneva, would give the President the flexibility he needs to break the arms control stalemate. Indeed, the declaration could provide an impetus for the summit meeting that President Reagan is seeking with Secretary Gorbachev.
Matthew H. Murray is a fellow at Columbia University's School of International and Public Affairs.