The Post's Dec. 17 editorial "Ban Underground Tests?" and Kathleen Bailey's op-ed column of the same day "This Is Not Arms Control" are both misleading.

Contrary to the editorial, nuclear testing is not needed to ensure the reliability of the U.S. arsenal. The image of government workers browsing through the storage racks to pull down a few samples to explode in order to check for "duds" is false, according to J. Carson Mark, former head of the Theoretical Division of Los Alamos National Laboratory. Testing for a statistically significant sample would require an impractical number of explosions and has never seriously been considered.

The few incidents in which testing proved useful in ferreting out defective nuclear warheads occured only because those weapons had not been correctly checked out before they were deployed. The lesson learned, Mr. Mark says, is not that we must continue exploding nuclear warheads, but that we should not deploy a warhead design until it's ready.

Kathleen Bailey complains that signatory nations of the Nuclear Non-Proliferation Treaty do not actually desire or expect the superpowers to end nuclear testing as required by the NPT. However, the preamble to the treaty specifically calls for an end to testing, and subsequent treaty review conferences have consistently demanded that the superpowers complete a comprehensive test ban as their part of the bargain with countries pledging not to pursue nuclear weapons.

Recent arms control accomplishments, such as the INF and START treaties, are not sufficient. As welcome as they are, such treaties only address the quantitative arms race. But a comprehensive test ban does more by addressing the qualitative arms race. It stops the development of new types of nuclear warheads. And that is the first step to meaningful disarmament -- and a more peaceful world. DANIEL YOUNG President Physicians for Social Responsibility Washington