Two more treaties to ratify

THE US Senate has another opportunity to contribute to progress in arms control: It should ratify the Threshold Test Ban Treaty of 1974 and the Peaceful Nuclear Explosion Treaty of 1976. The treaties set a 150-kiloton ceiling on the explosive force of nuclear-test devices, roughly 10 times that of the two bombs used on Japan during World War II.

The Threshold Test Ban Treaty was designed to steer the US and Soviet nuclear arsenals away from multimegaton warheads. By putting a 150-kiloton cap on nonmilitary nuclear explosions, the Peaceful Nuclear Explosions Treaty closed a potential loophole that might have allowed each country to test more powerful devices under the guise of using them for civilian applications.

Though both treaties are important, of greater interest is the Threshold Test Ban Treaty. Up to now, the United States and the Soviet Union have adhered to the pact, so why ratify it?

Some hold that ratification would set in motion the verification procedures, which include swapping detailed data on each country's test sites. This would improve the accuracy of monitoring efforts. That is a good reason, although the two countries are getting ready to, in effect, exchange test-site data anyway, the result of an agreement signed at the recent Moscow summit.

Of arguably greater long-term import is the treaty provision that puts each nation on record as working toward an eventual ban on nuclear testing.

In 1982, President Reagan put comprehensive test ban talks on ice until better ways to verify compliance with the existing though unratified treaties could be developed. In the meantime, the administration has consistently held that the Soviets have repeatedly violated the 150-kiloton limit.

For years many members of the science community have correctly called Mr. Reagan's plea for improved verification a red herring. That view received added weight recently from the congressional Office of Technology Assessment. It made two broad points: (1)Existing data show that the Soviets have been faithfully adhering to the existing testing limits; (2)seismic technology - most often used to measure earthquakes - can monitor tests with a high degree of confidence down to about 5 to 10 kilotons.

The administration should support rapid ratification of these two treaties. Indeed, it would be a fitting close to Reagan's tenure not only to receive credit for working toward cuts in existing strategic and medium-range nuclear weapons, but to reopen talks on a comprehensive test ban as well.