The article titled ''Scientists Propose Experimental Deep-Sea Dumping of Garbage'' {Jan. 11} raises the specter of returning to the oceans as the ultimate garbage can for wastes generated on land. The proponents of garbage dumping at sea make several unsubstantiated and scientifically indefensible assumptions about the safety and validity of such an activity. In one scenario cited in the article, 10 million tons of garbage would be ocean-dumped over a 10-year period at a site ''far out'' in the Pacific or the Atlantic. This large-scale dumping would masquerade a new policy as an ''experiment'' to use the oceans as marine landfills.

There are several problems with waste dumping at sea. First, the oceans are by their nature extraordinarily dynamic areas, subject to current, wind, storm and wave action that create a constantly changing environment. Dumping in the sea and expecting the sea to be stationary is analogous to assuming that air emissions will hover directly above a smokestack.

This state of flux leads to the second problem, which is the inability to adequately monitor ocean dump sites -- particularly deep-water sites -- for impacts in the direct dumping zone and adjacent areas. Few of the current 109 U.S. ocean dump sites are adequately monitored for impacts, and those that have been extensively assessed -- most notably, the 12-mile site off New Jersey -- have revealed profound impacts on commercial and recreational fisheries from exposure to pollutants in the materials that have been ocean-dumped. Yet the architects of the newest proposal advocate ocean dumping of garbage that is often laced with household and industrial poisons, sewage sludge, industrial wastes and toxic ash.

A third problem with the proposal is the assumption that the deep ocean, which would host the garbage site, is devoid of life and can therefore be used as a sacrifice zone for humanity's wastes. There is strong scientific evidence that the deep ocean, far from being a desert, is an integral component of a healthy marine ecosystem that deserves as much protection as the coastal zone.

Fourth, the proposed ocean dumping would fly in the face of U.S. law and prevailing public opinion. Reacting to public outrage over garbage and waste wash-ups, Congress passed the Ocean Dumping Ban Act in 1988, which bans sewage-sludge and industrial-waste dumping by 1992. To begin new dumping activities, this law would have to be modified, overturned or circumvented -- perhaps by characterizing dumping 10 million tons of waste as an ''experiment'' or ''research activity'' as the proponents seemingly are.

It is not scientifically or philosophically defensible to make the oceans into the world's greatest scrap heap. Problems with garbage disposal cannot be ameliorated by dumping in water: what is problematic on land is problematic at sea. The only real solution to our waste crisis is source reduction, not passing the buck from land to sea.

BETH MILLEMANN Executive Director, Coast Alliance SARAH CLARK Staff Scientist, Environmental Defense Fund Washington