PRESIDENT Reagan has made the appropriate decision in continuing to comply with the unratified SALT II. The resolve to stay within the treaty's missile limits is a victory for the moderate voices within the administration; it also keeps the United States in step with the wishes of its NATO allies. Politically, the decision runs counter to the desires of conservative supporters of Mr. Reagan. The treaty is not ideal, as the President has pointed out in the past. But it is preferable to have one arms limitation treaty in place than to have none at all. Each side has accused the other of violations of this and other arms limitations treaties, yet each has stayed within the limits of SALT II on the permissible number of ballistic missiles.
The President has left himself flexibility by saying that the US would keep open the option of ``proportionate responses'' to any Soviet violations. This puts pressure on the Soviet Union to hew to the provisions of the 1979 agreement.
Had there instead been a presidential decision to scrap the treaty, one result would have been to place another roadblock in the way of progress in the three-part nuclear weapons negotiations in Geneva, now stymied by disputes over the President's Strategic Defense Initiative, often referred to as ``star wars.''
Further, such action would have made a meeting more difficult to arrange in the short run between the President and Soviet leader Mikhail Gorbachev, and the leaders of the world's two most powerful nations ought to arrange a get-together.
Casting aside the treaty might have been more in the Soviets' interests than in America's, as the USSR is believed able to increase almost immediately the number of its land-based missiles above the 820-missile ceiling for that category.
By contrast the US has 270 fewer land-based missiles than the treaty allows, with a larger percentage of US missiles stationed aboard submarines.
The presidential decision is effective only for the short run. SALT II, although never ratified by the US Senate, expires at the end of this calendar year, and no one can be certain what will happen then. Both sides might continue to honor its numerical missile limits anyway, or they might not.
It will be preferable if progress has been made by year's end on the complex nuclear and space arms negotiations being held in Geneva. ``Star wars'' research apparently is the sticking point, with the US insisting on conducting it and the Soviets opposing such US research.
If only for purposes of self-protection, the US is correct in undertaking some ``star wars'' research. The Soviets are widely believed to have been researching the same issue themselves. Yet there might be some give and take in the amount of research that a future agreement would permit. Such a concept is worth exploration by both sides.