The future of arms control appears to hinge on the key question of what the superpowers will be permitted to test in space. Soviet leader Mikhail Gorbachev says the US must confine the Strategic Defense Initiative (SDI) -- the space-based missile defense system -- to research in the laboratory if he is to agree to sweeping reductions in offensive nuclear weapons. But what is ``laboratory research?'' Does that rule out all testing in space?
That is one of the crucial questions left unaddressed in Reykyavik, Iceland.
Administration officials and independent arms experts say the two sides must now come to grips in Geneva with the issue of the interpretation of the Anti-Ballistic Missile (ABM) Treaty. That pact prohibits the testing, development, and deployment of defensive systems or components in space.
``The treaty clearly limits SDI, but development is not a clearly defined word,'' says Mark Garrison, director of Brown University's Center for Foreign Policy Development. ``Lying behind what the Soviets are saying is a desire to pin down what the ABM treaty means.''
Originally the President said he would abide by the strict interpretation of the treaty, which Republican and Democratic administrations have observed since 1972 and which bars development of SDI. But he has placed a different legal interpretation on the pact and, according to aides, he wants to shift to that interpretation as the SDI program progresses.
``His interpretation is doubtful,'' says Alton Frye, an analyst at the Council on Foreign Relations. ``But even if he is determined to go forward under the loose interpretation there has to be a definitional clarification.''
Among the ambiguities is the word ``components.'' Experts believe the term provides an opening for resolving the Iceland deadlock. It could be clarified to permit many of the experiments that Reagan wants, such as testing of a laser in conjunction with a space-based mirror. But it could rule out major components of an SDI system which would not be ready for testing in the next decade.
``What President Reagan would have to give up is not his dream of a perfect defense but the crash `star wars' program, including a number of `space spectaculars' -- experiments conducted not for technical or scientific value but to maintain the momentum of the program for budgetary purposes,'' write experts Antonia Handler Chayes and Abram Chayes in the New York Times.
Arms control observers are encouraged that Gorbachev appeared to leave open the door to compromise. In his news conference following the Iceland meeting he said he had given the President a written proposal on the last day to prohibit ``testing of all space elements of antiballistic defense in space . . . except research and testing in laboratories.''
The term ``elements'' could be defined to permit testing of most of the present SDI program. Arms experts point out that much of the program, such as ground-based rocket interceptors, does not involve deployment in space. And some SDI space components could be restructured to be tested from the ground or in a laboratory.
``There is room for compromise,'' says John Pike, associate director of the Federation of American Scientists. ``Gorbachev could recognize that in practice some SDI stuff will take place in the field outside the laboratory -- and the question is to define what. And Reagan could order big chambers to be built in order to keep some experiments in the lab.''
The task, says Pike, will be to draw the line between SDI research that cannot be distinguished from other scientific research and SDI development that clearly has no other purpose. But the ABM treaty already sets a precedent for drawing such distinctions by establishing numbers above and below which certain land-based ABM components cannot be developed or deployed.
``So what would be required is to pick some new numbers for the new technologies -- and that's where Gorbachev could give,'' says Pike.
Behind the Iceland deadlock lie profound Soviet concerns about the SDI program. The Soviets think the US is trying to gain nuclear superiority because SDI is viewed as militarily useful only in connection with a first strike. Gorbachev and his colleagues also worry that SDI unleashes a technological race in space which the Soviet Union will have trouble keeping up with.
If the controversy over the ABM treaty can be worked out, there remains the issue of SDI deployment. Some analysts think the Soviets will insist that the US agree not to deploy an SDI system at the end of 10 years except on mutual agreement.
``It would take very little adjustment on the President's part to achieve a strategic arms agreement,'' says John Steinbruner of the Brookings Institution. ``If he agreed to deployment of SDI by mutual agreement only . . . the Soviets would give him some field testing.''
But other specialists think this issue could be finessed by saying that SDI deployment would be subject to mutual discussion. ``Reagan could say, `Our hands are free to deploy' and Gorbachev would say `We have to be a part of the decision,' '' suggests John Pike. And by then, he adds, the issue might be moot.
Technically, say experts, a compromise is doable. The more difficult problem is political, i.e. the perception with which each leader emerges from an agreement. Gorbachev must be able to say that he got something on the critical issue of SDI and President Reagan must be able to say that his visionary program is intact.
``Both leaders have started out with firm positions rhetorically and that may make it difficult to come up with a compromise position,'' says Pike.