The dangers of tampering with SALT

The effect of President Reagan's Memorial Day weekend announcement on strategic arms control is to keep intact, for the time being, the ten-year old SALT framework while the two superpowers begin new START discussions on June 29.

However, the Reagan administration at the same time is laying down a marker which, in the interest of preserving military options, reserves the right to take actions in the next few years that may be inconsistent with previous SALT agreements. One example is the construction of new, fixed ICBM silos that would be required if the latest scheme for basing the MX missile -- ''dense pack'' -- is adopted. SALT prohibits the building of any additional fixed ICBM launchers and the relocation of existing ones.

The new ICBM complex, for which holes could be dug as early as 1984, will be described as requiring only minor technical revisions in the SALT II treaty articles due to expire in 1985. Secretary of Defense Weinberger says it is ''a matter of interpretation.'' But, of course, the Soviets will get something in return for any deviation in the SALT regime.

There is another, more binding, agreement with the Soviets. Even though the Arms Control and Disarmament Agency has locked up copies of the 1979 SALT II treaty and explanatory documents, perhaps Director Eugene Rostow will permit public distribution of the text of the 1972 Treaty on the Limitation of Anti-Ballistic Missile Systems and the subsequent 1974 protocol to it. The ABM agreement was written for ''unlimited duration'' though subject to amendment and five-year interval review. It is a model of a tightly drawn, clear and simple arms control and reduction agreement -- by comparison with those limiting offensive arms. The treaty forbade the deployment of ''ABM systems for a defense of the territory'' of the US or the Soviet Union. Thus, each side agreed to keep its defenses down against strategic offensive missiles, by limiting themselves to one (''a single area'') constricted ABM site. Each party undertook ''not to interfere'' with the national technical means of verification (satellites, etc.) which are used to provide assurance of compliance.

The ABM treaty has relevance for Reagan's latest MX missile basing plan, which envisages some form of ballistic missile defense for the new ICBM. While any defensive system designed to protect MX -- under ''dense pack'' -- would presumably require only one ABM site, the negotiating history of the treaty will not sustain the argument that the present deactivated site at Grand Forks, N.D. can be scrapped for a new one around our newest and biggest land-based missile. The 1974 protocol to the treaty states that an exchange of sites may be exercised ''only once'' by each side and then reads: ''The US would have the right to dismantle or destroy the ABM system . . . in the deployment area of ICBM silo launchers and to deploy an ABM system . . . centered on its capital.''

The same article of the protocol states: ''The Soviet Union would have the right to dismantle or destroy the ABM system and its components in the area centered on its capital and to deploy an ABM system or its components in an area containing ICBM silo launchers. . . .'' How would we react if the Soviets decided to relocate their Moscow ABM system and place it around one of their ICBM complexes, even though -- clearly -- they are permitted to make such an exchange?

The real internal policy of the government -- which will become more obvious with the President back from Europe - is to pursue future military options without reference to SALT II or the ABM part of SALT I. The Reagan administration will cross the bridge of ''breakout'' when they get to it. In the meantime, they will hope to lever the Soviets to give up more in START negotiations because of an uncertain trumpet on the long-term viability of past SALT agreements.

The only problem with this tactic is that the Soviets can do some levering of their own outside a formal treaty. For example, they could threaten to increase the warheads of their 308 SS-18's from an assumed 10 each to 20, 30, or 40 per missile. This would knock the grand total of warheads Reagan wants to reduce by one-third into a cocked hat. And the Soviet lead in land-based missile warheads -- which Reagan wants to reduce to 50 percent of the lowered overall total of missile warheads -- would be even more disproportionate so as to put his goal practically out of reach.

Further, if the Soviets choose to develop more than one new type of ICBM -- one is all that is allowed under SALT II -- the President's goal of reducing all intercontinental missiles to one-half of the current US level will be jeopardized.

To proceed with the MX is to proceed with an ABM system of some kind not permitted under the ABM treaty. Further, to proceed with the MX missile, to be based in a new field, is to undercut a provision of SALT II that was part of a package of restrictions originally designed to check the Soviets. (Taken together, the Article IV limitations on fixed launchers of ICBMs were meant to prevent the Soviets from increasing the number of their heavy ICBM silo launchers.)

The most serious blow that could be struck against controlling strategic arms would be for the Reagan administration to tinker with the ABM treaty. If the new system were to be a mobile one -- now prohibited -- such a development would almost guarantee destablizing deployments on both sides. If the new system were to be a very limited one -- say, 100 interceptors to protect 100 MXs -- the US could not be sure that the propective gains in ICBM survivability were enough to balance the risks of corresponding but different Soviet ABM actions.

''Technical adjustments'' in treaties -- which some in the administration will describe as ''minor'' -- can mushroom into new rounds in the arms race that can leave us in a more dangerous posture, even if and especially if they are acceptable to the Soviets. And even if we are seeking them only for the ''limited purpose'' of trying to ensure land-based missile survivability in the age of MIRVs.

Better to cling to the known of treaties agreed to, and understood by, the two superpowers than to unravel them for unknown marginal and temporary military advantage.