The United States and the Soviet Union have edged closer to agreement on medium-range nuclear missiles - and thus a superpower summit - after a further arms control concession by Moscow. Speaking to a press conference yesterday shortly before leaving Moscow after three days of talks, US Secretary of State George Shultz said that ``considerable headway'' had been made on the subject. ``With hard work and creative effort,'' he said, an agreement was possible.
The next stage in the process will come in Geneva next Thursday, when Soviet and US negotiating teams resume their discussions.
Soviet officials say that they believe an agreement on medium-range missiles is possible by the end of the year. And, they add, that would be enough to bring Soviet leader Mikhail Gorbachev to the US for a summit.
The breakthrough seems to have come Tuesday, when the Soviet leader told Mr. Shultz that Moscow would eliminate shorter-range nuclear missiles in Europe within a fixed time period, since confirmed to be one year. The US and NATO had previously voiced concern that elimination of medium-range missiles alone would lead to a European balance of nuclear power in favor of the Soviet Union.
Shultz cautioned, however, that he would have to consult carefully with the US's NATO allies on the new proposal. In fact, he flew directly from Moscow to Brussels, where he will brief NATO officials.
The attitude of some West European nations could complicate an agreement. Britain and France, which have their own missiles, and West Germany, which is the site of many US nuclear weapons, are all known to be ambivalent about drastic cuts in the nuclear weapons.
Soviet officials made it clear that they saw no reason for the US to hesitate.
``There is nothing left for them to object to,'' said an official immediately after the Shultz press conference. ``We have made all the concessions they have asked for.'' The caution with which Shultz welcomed the latest Soviet move, the official commented, was therefore ``suspicious.''
Soviet officials also claim that while their side offered a series of new proposals, ``Shultz offered nothing - except reducing the time they would observe the Anti-Ballistic Missile Treaty.''
Shultz told journalists that the US had proposed that both sides adhere to the treaty for seven years, until 1994. The previous discussion of a 10-year period, he said, was based on the assumption that strategic missiles would be completely eliminated during that period. Now a 50 percent reduction is being discussed.
Shultz told the press conference that less progress had been made in other areas of arms control. He noted, however, that both sides had agreed on the need for a comprehensive ban on chemical weapons, though they did not agree on verificiation methods. Shultz added that he and Soviet Foreign Minister Eduard Shevardnadze had agreed that their respective experts would visit each other's chemical weapon destruction plants. Gorbachev announced last week that such a plant was under construction.
In addition to conceding the issue of shorter-range missiles, Gorbachev offered during Tuesday's talks a clearer definition of another subject that has bedeviled US arms talks since the Reykjavik, Iceland, superpower summit last October: the Soviet definition of laboratory research on the Strategic Defense Initiative (SDI, or ``star wars'').
At Reykjavik, the Soviets had called for SDI research to be confined to the laboratory. The definition of laboratory has since then been the subject of considerable debate.
An official Soviet account of the Gorbachev-Shultz talks, published yesterday in the Communist Party newspaper Pravda, quotes Gorbachev as saying that the term covers research ``on Earth - in institutes, testing grounds, factories.'' Gorbachev also called for consultations on the type of devices whose deployment in space would be prohibited - a clear hint that Moscow was ready to consider the deployment of some sort of SDI-related instruments in space.
Shultz appeared unmoved by the new definition. ``In the field of space, we have not made much progress,'' he told the press conference.
The Soviets may have made one other breakthrough of a more intangible nature. Some senior US officials have in the recent past expressed skepticism about the changes in the Soviet Union. Shultz, however, seemed impressed.
``It's quite clear that important changes are taking place in the Soviet Union,'' he told journalists. ``We're looking very carefully at the interesting developments taking place across the board'' in the restructuring of Soviet society.
He was less pleased with the state of the new US Embassy.
There was, he said, a ``honeycomb'' of listening devices throughout the building which might require major structural changes to remove.
The Associated Press reports from Moscow: The Soviet Union and US yesterday signed an agreement on cooperation in space and the use of space for peaceful purposes, the Soviet news agency Tass said. Tass said the agreement was signed by Shultz and Mr. Shevardnadze, but provided no details of the agreement.
One key area of dispute between the US and Soviet Union in arms control is the American ``star wars'' research program for a space-based anti-missile system.
The Soviet Union says the program will lead to the militarization of space.