New arms pact hinges on 1972 ABM treaty. Changes may be necessary to clarify some ambiguous terms

The ABM treaty is emerging as a central element in the debate over an arms control agreement. As negotiators in Geneva focus on a new Soviet proposal on offensive nuclear weapons, arms experts warn that the United States and the Soviet Union are on the edge of undermining the 1972 accord limiting antiballistic missile (ABM) systems.

On the 13th anniversary of the treaty yesterday, six former US defense secretaries called on the superpowers to shore up the pact by negotiating new measures in Geneva.

Erosion of the pact has reached a ``crisis point,'' former Defense Secretary Harold Brown said on the CBS Morning News yesterday. Washington and Moscow ought to ``think carefully'' about how to reinforce a treaty that has helped stabilize the strategic balance and reduce the risk of nuclear war.

Both superpowers are faulted by ABM treaty supporters: the Soviets for deploying systems not allowed under the treaty, including a large phased-array radar near the central Siberian city of Krasnoyarsk; the Americans for planning tests of systems under the President's Strategic Defense Initiative (SDI, also called ``star wars''), which will soon encroach on the treaty.

Included in such US testing is ``Talon Gold,'' the pointing and tracking portion of a space-based laser; the Airborne Optical System (AOS), an infrared telescope carried aboard an aircraft to track and identify warheads above the atmosphere; and the electromagnetic rail gun, which accelerates projectiles to high speeds to incercept missiles.

President Reagan maintains that research on his Strategic Defense Initiative -- which he says includes testing and development -- will not violate the ABM treaty. According to US officials, he has directed that the SDI plan be conducted in full compliance with it.

But many Western specialists, as well as the Soviets, are skeptical. Testing and development of technologies for a space-based defense shield, they say, not only will preclude an agreement with Moscow on reductions in offensive nuclear weapons. It will be inconsistent with the ABM treaty.

American officials acknowledge that the larger role for defense envisioned under SDI will eventually require amending or scrapping the treaty. A recent study by the Office of Technology Assessment also notes that the US must eventually choose between seeking Soviet agreement to revise the treaty or withdrawing from it.

Under current plans for SDI technology testing, the US will be in violation of the treaty by 1990, and perhaps as early as 1987, arms experts say.

But there is considerable controversy arising from some imprecise language in the treaty.

The treaty, for instance, allows research on all types of ABM systems and components. But under Article V, each party undertakes ``not to develop, test, or deploy ABM systems or their components which are sea-based, air-based, space-based, or mobile land-based.''

What does ``develop'' mean?

During the SALT I negotiations the parties never agreed on an interpretation of the term. A Pentagon statement in 1972 to the Senate Armed Services Committee made a distinction between exploratory and advanced development (which preceded field testing) and engineering development. The latter was deemed prohibited. But the Americans and Soviets have not agreed on a definition.

What does ``component'' mean?

During the treaty negotiations the two sides discussed the difference between a ``component'' and an ``adjunct,'' which would not be prohibited by the treaty, but no formal agreement was reached.

Now the US is developing SDI technologies, such as AOS, which it says are ``adjuncts'' because they are not components standing on their own, that is, ABM missiles, launchers, or radars as mentioned in Article II.

Ambiguities also exist over the phrase ``tested in an ABM mode'' as applied to types of missiles and radars limited by the treaty.

The whole point of the ABM accord was to keep each side vulnerable to retaliation and thereby deter a first strike. Under the pact, each side is limited to one fixed, land-based ABM site, either to defend the national capital or one ICBM field.

The Russians installed a system around Moscow; the US chose to dismantle its system -- in effect acknowledging the overwhelming force of offensive nuclear weapons given the state of defensive technology at the time.

Since 1972, however, there have been huge advances in defense technologies (such as sensors, computers, directed energy, and space transport). Many Pentagon and administration officials now believe nuclear deterrence could be improved on both sides by defensive systems.

The fact that the Soviets are upgrading their permitted defense system and conducting their own research on space weapons suggests they might agree to modify the ABM treaty if the US agreed to SDI limits.

``As part of a general negotiation in which there were limits placed on SDI, the Soviets would likely be prepared to consider such revisions in the treaty,'' says former Defense Secretary James R. Schlesinger. ``They want to preserve the treaty and if there were some adustments in definitions and wording, they would be willing to consider this -- and probably do it.''

The former defense officials issued their call under the auspices of the National Campaign to Save the ABM Treaty. Congressmen made similar statements yesterday in support of the pact.