Tokyo — The Japanese government, after receiving a detailed briefing on the Iceland summit from a top United States official, expressed support for the US stance. Prime Minister Yasuhiro Nakasone said that despite the breakdown of the talks at the final stage, the meeting had given arms reduction agreements a ``major push.'' Mr. Nakasone said, ``This progress, including the Soviet proposal for cuts in its SS-20 intermediate missiles deployed in [Soviet] Asia, was made possible, first of all, by the unity of countries in the Western camp.''
The Japanese were briefed by Amb. Edward Rowny, a top arms control official, who flew here from the Iceland meeting. After the briefing, Mr. Rowny told reporters here that ``the Japanese government . . . has expressed strong support for our continued allied solidarity.''
Tokyo has no apparent inclination to blame the Reagan administration for the failure in Reykjavik to reach an agreement on the controversial Strategic Defense Initiative (SDI) program. ``Well-informed people within the government think that the Soviet Union was asking for the impossible as far as SDI is concerned,'' a Japanese official said.
The Soviets will offer their version of what happened at Iceland starting Sunday, when Deputy Foreign Minister Mikhail Kapitsa visits Tokyo for three days of meetings with government officials.
The Soviets are expected to stress the SDI issue. The research program is still a sensitive political question in Japan even after the government's decision to join the research program last month.
``There will certainly be intensified debate [by opposition parties in parliament] over the wisdom of Japan's participation in SDI, an official predicted. ``We will answer that it was SDI that enabled such Soviet concessions and forthcoming attitude'' on other arms issues at Iceland, the official said. The US-Soviet impasse, he insisted, will ``have no impact whatsoever'' on Japan's participation in SDI.
Japanese officials generally agreed with Rowny's optimistic view that the differences on ``many issues were narrowed.'' At the Reykjavik summit, Rowny insisted, ``time just ran out.'' He added: ``I remain optimistic that a way can . . . and will be found, to reach agreements.''
The key arms control issue for Japan is that of intermediate-range nuclear forces (INF), particularly Soviet SS-20s based in the Asian part of the Soviet Union.
In Iceland, according to Rowny, the two sides agreed on a formula that would reduce medium-range missiles to zero in Europe and leave 100 warheads in Soviet Asia and in the US, ``as an interim step to the complete elimination of all these weapons.'' This formula, although it leaves some weapons in Soviet Asia initially, is apparently acceptable to Tokyo.
``If everything is realized based on the American proposal,'' a Foreign Ministry official commented, ``particularly in the area of deep cuts in INF, it would be appreciated by our government.'' The Japanese, Rowny commented, ``stress as we do that these are interim steps on the way to complete reductions.''
There is concern in Japan, though, that the potential INF agreement may depend on solving the more intractable SDI issue. At the Reagan-Gorbachev summit last year, the two sides had agreed to keep those problems separate. Also at Iceland, Rowny claims, ``there was no linkage [made] during our discussions.'' Only lack of time stood in the way, he argued.
The ultimate Japanese view, however, may depend, as one official put it, on ``whether you believe in the US interpretation [of the Iceland meeting] that future negotiations can be picked up where you left off in Reykjavik.''