In their letter {"They're Oceans, Not Garbage Dumps," Jan. 26}, Beth Millemann and Sarah Clark have fired a broadside at those who advocate deep ocean waste disposal. Typically, all of their shots missed the target.

Their understanding of ocean dynamics is simplistic, demonstrating a lack of knowledge. Scientific investigation undertaken by the best over many, many years has disclosed that while large areas of the ocean depths are quiescent with scarely any movement or life (marine or human), other parts are so soiled by naturally produced highly toxic chemical, metallic and radioactive daily discharges that the introduction of waste deposits would be scarely noticeable.

The writers appear to assume that raw, unprocessed waste would be surface-dumped into the seas at indiscriminate locations. Such is not the case. I made the effort to find out -- why couldn't they? The responsible program under consideration by the world's most eminent scientists requires that the waste first be processed to an irreducible minimum by recycling, then that the remaining bulk be converted to compost. This residue would then be delivered to predetermined areas and deposited into deep ocean "mud banks" by special deep deposit autonomously powered "bells."

To suggest that source reduction is the only acceptable method of solving the waste disposal problem betrays a refusal to meet the realities of the problem head on. The ever increasing world population alone is enough to ensure their objective could never be met. The time to come to grips with the waste disposal problem is now, with an approach that has been scientifically determined to inflict an absolute minimum of damage on the environment and on human health. The environmentalists owe it to themselves to at least make an honest appraisal of this technology, or the only thing they will shoot is themselves, in the foot.

HAROLD C. PETROWITZ Washington