The Soviet Union is stepping up its pressure on the Reagan administration to halt nuclear weapons tests, and is implicitly linking this year's summit meeting to agreement on the issue. The move could be part of a subtle tactical shift in Soviet foreign policy. Instead of emphasizing his opposition to ``star wars'' -- a space-based defensive system that the United States is now studying -- Soviet leader Mikhail Gorbachev is underscoring opposition to nuclear testing altogether.
The issue was important enough for him to make a nationwide television address Saturday, calling for a quick meeting with President Reagan to work out plans for banning nuclear tests. The White House quickly rejected the call.
Left uncertain, however, is the impact of all the back-and-forth talk on this year's planned summit meeting.
A ban on nuclear testing would, according to some experts, have the same practical effect as hampering research on the Strategic Defense Initiative (SDI, or ``star wars''). Some elements of a space-defense system might employ high-energy weapons, some of which might be powered by nuclear explosions. The US is conducting tests on some of the new-generation nuclear devices that might be involved in SDI.
Thus the Kremlin, having failed to derail SDI directly, and finding it difficult to rally public opposition to what the US contends is a defensive weapons system, now seems to be targeting the US nuclear-weapons testing program.
In his televised address, Mr. Gorbachev called for a halt to nuclear testing by both superpowers and an agreement to halt future tests. The Easter weekend move came just as the European peace movement is reawakening from winter hibernation and a unilateral Soviet moratorium on nuclear tests is set to expire.
At their November 1985 summit in Geneva, Gorbachev and Mr. Reagan agreed to meet this year in the US. But the Soviets have yet to agree to a date. They cite the need to make substantial progress on arms control at a summit. On Saturday, Gorbachev proposed to meet with Reagan in Europe. He left it unclear whether such a meeting would be instead of, in addition to, or a prerequisite for a later summit in the United States.
Gorbachev said a meeting with Reagan should take place ``in the nearest future, in London, Rome, or any other European capital.'' And, he said, it should be for the sole purpose of ``putting an end to nuclear testing.'' But he said nothing about plans to visit the US later this year.
The White House says no summit should have such a narrow focus. It said that the next summit should cover all the issues in superpower relations.
``Nuclear testing is one of them -- but only one. And it is an issue that is directly related to others such as the need . . . to reduce levels of existing nuclear arms and to establish effective verification procedures,'' the statement said. It was issued in Santa Barbara, Calif., where the Reagan is vacationing.
Gorbachev also stressed that the Soviet Union's moratorium -- due to expire with the first US nuclear test held after next Monday -- will not be extended.
``This must be absolutely clear,'' said Gorbachev. After March 31, Gorbachev said, the Soviet moratorium would only be observed so long as the US refrains from nuclear testing.
Earlier, a US State Department spokesman confirmed that the US is planning a nuclear test during the third week in April. The first US test of the year, conducted March 22, prompted harsh Soviet criticism. Gorbachev, in his speech, called the American refusal to join in a moratorium a ``pointed challenge'' to the Soviet Union and other countries.
The White House, in its response to the latest Gorbachev statement, repeated offers to share new technology for verifying a moratorium and for convening a panel of experts from both countries to discuss verification problems.
Earlier, the Soviets had dismissed the offers as ``political tricks.'' The US has indicated that verifying compliance with a moratorium is a serious obstacle to arms control. The Soviets have derided that argument, but so far have not been willing to enter into technical negotiations to verify whether or not countries are conducting nuclear tests. Reagan has offered to allow Soviet experts to view US nuclear tests and calibrate their instruments in order to aid future verification, but the Soviets have declined.
Gorbachev's delivery was calm, self-assured, and evenly paced. Even though he made some strong charges against the US administration, he made them in a controlled, low-key manner. Pravda, the Communist Party newspaper, had taken the unusual step of alerting television viewers to the speech in advance. Ordinarily, a Soviet leader's television appearances come as a surprise. Foreign television correspondents were even encouraged, in advance, to make bookings of satellite time in order to relay reports about the speech to the West.
Still, Gorbachev denied that he was trying ``to gain extra propaganda `points,' as journalists say in such cases.'' That consideration, he said, had received ``the least of [our] thoughts.''
Some Western Kremlin-watchers here are unconvinced. While admitting that Gorbachev's presentation of the Soviet position is becoming more effective, they say he seems to prefer sweeping gestures rather than the detailed work of actually fashioning arms control agreements.
What seemed most puzzling was his omission of specific reference to the planned summit in the US this year. The only reason he gave for calling for a quick meeting in Europe was that ``the situation requires immediate action.''
Some analysts believe the ambiguity on this point was calculated -- an attempt to avoid a committment to visit the US in an effort to build up pressure on Reagan to halt nuclear tests. On the other hand, by not explicitly stating that, Gorbachev avoids the accusation that he is waffling on his earlier agreement to a summit. And he can still visit the US later this year without appearing to have given ground to Reagan or losing face.