Two new studies dispute President Reagan's suggestion in recent weeks that Soviet underground nuclear weapons tests may have violated the limits of a 1974 treaty.
The studies by geophysicists at Columbia University, the University of Colorado and the U.S. Geological Survey found that the Soviet tests have fallen within the 150-kiloton explosive limit imposed by the Threshold Test Ban Treaty.
"Over the past five years the size of the largest Soviet tests come very close to 150 kilotons, but none appear to have exceeded the limit," Columbia professor Lynn R. Sykes said in an interview.
Reagan said last month that there was "reason to believe that there have been numerous violations" of the treaty but offered no evidence.
An administration official said last night that "we have never made the allegation" that the Soviets violated the treaty, but "we do have concerns that there may have been tests in excess of the limit." The official added that verification procedures "are not sufficient" to provide absolute proof. Last year, criticizing verification procedures in the 1974 treaty and citing the need to test new weapons, the Reagan administration decided not to resume talks with the Soviet Union and Great Britain on a comprehensive test ban treaty begun in the Carter administration.
The administration instead sought revision of the 1974 agreement because of concern that the Soviets may have detonated weapons larger than the accord allows.
The Soviets refused to renegotiate, calling instead for resumption of the comprehensive test ban negotiations.
Sykes was a member of the U.S. team that negotiated the 1974 treaty and is widely regarded as one of the nation's top seismic scientists. He conducted extensive research for the Air Force in the 1970s on underground test detection, and is an adviser with the Defense Advanced Research Projects Agency (DARPA).
Sykes and co-author Ines Cifuentes of Columbia's Lamont-Doherty Geological Observatory presented their findings yesterday at a meeting of the American Geophysical Union in Baltimore.
In a summary of his technical paper, Sykes said in an interview that the allegations made by Reagan and others "are based on a systematic overestimation of the relation between seismic magnitude and explosive yield," an effect he attributed to the different geologic characteristics of the Soviet and U.S. test sites.
A second paper challenging the suggestions of treaty violations was presented by Dr. Charles B. Archambeau of the University of Colorado and former DARPA scientist Dr. Jack F. Evernden, now a senior researcher for the U.S. Geological Survey in Menlo Park, Calif. "Based on both seismic body and surface wave magnitude estimates, the U.S.S.R. appears to be complying with the 150-kiloton limit," the report said.
The scientists' conclusions are supported by a classified study conducted for the Defense Department at the Lawrence Livermore National Laboratory in California, according to sources there.
"Whatever it is believed in Washington, it is now clear that officials here at Livermore lab do not believe that the Soviets have violated the 150-kiloton limit," a Livermore physicist said.
"We even show violations for some of our own shots" when estimating from the seismic data, added Robert W. Alewine of DARPA in another presentation. "One looked as high as 265 kilotons," he said, "and the Russians called us on that one."
Although Alewine agreed with Sykes, Evernden and others about the need to correct for the different geologic characteristics of the U.S. test site in Nevada and the test sites in the Soviet Union, he used a correcting factor half that employed by Sykes. Using this approach, he said, the largest Soviet test was calculated at about 300 kilotons.