Swap A-Test Sites, Soviets Urge U.S. : Plan Could Tighten Verification, Ease Path to Arms Pact, White House Says

In a move that may narrow a superpower dispute over limiting nuclear tests, the Soviet Union has proposed that it and the United States explode atomic weapons at each other’s underground test sites to improve ways of detecting and measuring the blasts, U.S. officials said Saturday.

The Reagan Administration, reacting positively, indicated that the offer might ease U.S. complaints about the accuracy of present means of verifying nuclear tests. Those doubts have blocked U.S. approval of 1974 and 1976 treaties limiting the number and size of both nations’ underground tests.

“Whether we can get an arrangement that gives us that kind of thorough verification remains to be seen,” Kenneth L. Adelman, director of the U.S. Arms Control and Disarmament Agency, said in a Saturday television interview. “But we’re moving down that road. That’s the big message.”

‘Interesting Idea’

Secretary of State George P. Shultz told the Soviets last week that the swap is “an interesting idea,” and the two sides agreed to discuss it at talks among nuclear test experts next month in Geneva, said a White House official in Santa Barbara, speaking on a condition of anonymity.

The Soviet offer was made to Shultz last Tuesday during arms-control talks in Moscow. It apparently would allow each nation to explode weapons of predetermined yields at the other’s test site.

Each nation would test its own nuclear devices and its own monitoring equipment during the explosions. Scientists would use the blasts to gather geologic and seismic data, calibrating equipment that then could be used to monitor future nuclear blasts.

Both sides already monitor tests from afar, but the United States says those measurements are not accurate enough to guarantee compliance with the 1974 and 1976 pacts, the Threshold Test Ban Treaty and the Peaceful Nuclear Explosions Treaty.

Limit of 150 Kilotons

Those agreements limit underground nuclear explosions to a yield of no more than 150 kilotons, or 150,000 tons of TNT. The Hiroshima atomic bomb had a yield of about 13 kilotons.

The Reagan Administration, which recently sent the treaties to the Senate for ratification, has insisted on more accurate verification as a condition of their implementation. The Soviets, meanwhile, have balked at U.S. proposals to monitor blasts by a system dubbed CORRTEX, in which an electrically charged cable is lowered into a hole at each test site.

The CORRTEX system measures the yield of explosions by detecting the rate at which the blast crushes the cable. U.S. experts say it would determine the yield of explosions to within 30%, a figure they claim is far more accurate than current estimates.

Additional Data

The Soviets, however, have apparently concluded that the system would give the United States access to more secret information than the mere yield of an explosion.

“What has been a question has been Soviet fear of our on-site inspection,” particularly fear concerning the non-yield information, the White House official in Santa Barbara said.

The Soviet offer appears similar to clauses in the 1970s treaties calling for one or two “calibration explosions” to gauge monitoring instruments before implementing the treaties, said Jack Mendelsohn, deputy director of the private U.S. Arms Control Assn.

The Soviet offer goes beyond that clause, however, by allowing nations to conduct on-site monitoring of the calibration blasts instead of relying on potentially altered data to calibrate their instruments.

‘Ceded a Little Ground’

The new offer “gives each side a graceful way to settle their falling out over the verification aspects of the treaty,” Mendelsohn said. By agreeing to on-site monitoring of a test, “the Soviets had ceded a little ground, and if the Administration has any grace, they’ll take it.”

Adelman, however, voiced suspicion on Saturday about the Soviets’ sincerity.

In an interview on Cable News Network’s “Newsmaker Saturday” program, he accused the Soviets of pulling back from their own proposal last week. He said that the initial draft of an agreement on the exchange was scrapped after Soviet officials objected to the wording of the last paragraph.

“We worked out a piece of paper that I thought was very good and very much in line with American national interests,” Adelman said. But after Shultz gave that paper to Soviet leader Mikhail S. Gorbachev last Wednesday, “the Soviets started walking back from the whole agreed language.”

He called the discussions “very frustrating.”

Meanwhile, Reagan, on vacation at his ranch 30 miles northwest of Santa Barbara, said that Shultz had made “constructive progress” in Moscow in the effort to reduce the superpowers’ nuclear arsenals and improve U.S.-Soviet relations.

Speaking in his weekly radio address to the nation, the President pointed out that in Moscow, the United States and the Soviet Union agreed that “a limit should be set on the number” of shorter-range missiles.

“A global framework will be the basis of discussion and . . . the principle of equality will govern,” he said.

In addition, he said, “both governments agreed to the principle of on-site verification” of adherence to an arms reduction agreement.

In Moscow, the central topic was the reduction of medium-range weapons--those that are deployed in Europe by the West and by the Soviet forces in Eastern Europe.

Optimistic Tone

Reagan, who, with his senior advisers, has spoken optimistically in the past days about Shultz’s talks with Gorbachev and Soviet Foreign Minister Eduard A. Shevardnadze, continued in the same tone Saturday.

He pointed out that when he met with Gorbachev in Reykjavik last October, an understanding was reached on the “basic tenets of an agreement to reduce intermediate-range missiles.

“In the intervening months, we have been encouraged by signs of Soviet willingness to remove the roadblocks that have been holding back progress,” Reagan said.

Later, Reagan made an afternoon visit to a camp, near his ranch, for children with cancer.

At the camp, he said: “There is great reason for hope. It’s the first time there has ever been a Russian leader who has actually suggested eliminating--doing away with--some of the weapons.”

‘A Little Superstitious’

Asked by a reporter about the prospects for a summit conference, Reagan said: “I feel very good. I’m also a little superstitious. I don’t want to talk about things until they happen.”

He also responded to 9-year-old Michael Covel of Riverside, who asked, “How’s Mr. Shultz doing on the ordeal . . . of nuclear missiles?”

Reagan replied, “He’s come home very optimistic, and we’re all looking forward to carrying this through to where we can make some start in eliminating these terrible ballistic missiles.”

The President began making contributions to the privately funded camp for young cancer victims after reading about it three years ago in Reader’s Digest. He used the visit to the camp, two miles from his mountaintop ranch, to espouse the virtues of voluntarism, but he also was asked about retirement.

“I have thought about the possibility of writing a book,” he said, “so that you could get the true story of what has been going on.”

Michael Wines reported from Washington and James Gerstenzang from Santa Barbara. Times staff writer Thomas B. Rosenstiel in Santa Barbara also contributed to this story.