US, Soviet scientists progress in nuclear test-monitoring effort. Russians in American West this week, choosing seismic sites

A delegation of Soviet scientists is in the United States this week, fulfilling the second part of a private arrangement with American counterparts to establish stations in both countries to monitor seismic activity - including any underground nuclear explosions. Last July American seismologists visited a remote region of the Soviet Union to install sensitive seismometers.

On Friday the spokesmen for the Soviet and American scientists will hold a press conference in Washington to announce the test sites. The five Soviet seismologists talked to reporters earlier this week at the Scripps Institution of Oceanography, a part of the University of California at San Diego, one of three US universities taking part in the historic arrangement. The others are the University of Colorado at Boulder and the University of Nevada at Reno.

The arrangement between American geophysicists and members of the Soviet Academy of Sciences bypasses official US channels.

US groups that favor an end to testing, such as the Natural Resources Defense Council (NRDC), an environmental advocacy group that is backing the monitoring effort, say it would be a way of halting the march of new technology that powers the arms race.

But the Reagan administration says that as long as the US depends on nuclear weapons for deterrence, tests are needed to ensure reliability of warheads in the stockpile and to perfect new weapons needed to balance the Soviet military threat.

The Soviets are backed by their government, which imposed a moratorium on nuclear testing 15 months ago in hopes of persuading the US to give up nuclear weapons testing.

The US government denied the Soviet scientists access to potential test sites in Nevada and California. The most likely choices form a triangle just south of Las Vegas, Nev., and north of Death Valley, hugging the California-Nevada border.

Test sites will be chosen by the Soviet specialists on the basis of data provided by their American counterparts.

``We will bring the sites to them by bringing the data out,'' said S. Jacob Scherr, an lawyer with the Washington-based NRDC, which has coordinated the seismic project.

Last spring NRDC staff scientist Thomas Cochran, an expert in arms control and nuclear nonproliferation, visited Moscow for an international conference on nuclear test bans. He recruited two seismologists from the University of California at San Diego, both professors at the Institute of Geophysics and Planetary Physics, to work with their Soviet counterparts on this plan.

Never before had Western researchers gathered strategically sensitive data on Soviet soil. The Soviets permitted Jonathan Berger and James Brune of San Diego to journey to the Kazakh Uplands near the Chinese border in the south-central Soviet Union to install temporary monitors.

The American scientists are scheduled to ship far more sophisticated equipment to the Soviet Union early next year. It will be placed in 300-foot-deep bore holes and underground vaults that the Soviets have already prepared for the Americans at a temporary station in western Siberia.

The Soviets have also built a laboratory and housing trailers for the scientists in a nearby city.

A stream of recorded data from both countries will be available to research scientists all over the world. Those involved say they expect to learn a lot about oscillations originating from nuclear blasts as well as from earthquakes. Reagan administration skeptics say the Soviets are using the scientific exchange program as propoganda to turn public opposition to nuclear war into a groundswell of sentiment against the US.

Ironically, the US has twice invited Soviet scientists to witness nuclear explosions and both times has been refused, Mr. Scherr said. The American scientists who went to the Soviet Union in July were not given access to sites in the vicinity of nuclear testing facilities.

The NRDC has raised $2 million to fund the project, including the installation of equipment that one researcher called ``the best in the world.'' The Soviets were to visit Dallas Wednesday and Thursday to inspect the equipment.

``When we went over in May, we said to our Soviet colleagues that we don't have to wait for the political issues to be solved. Let's go ahead with the technical issues,'' Mr. Cochran said.