The otherwise excellent news story "'72 Diet Pill Ban Ignored Until Recent Deaths" {front page, Sept. 4} failed to note an important fact: the strain of bacteria used to produce batches of L-tryptophan that have been associated with 27 deaths and 1,500 cases of eosinophilia myalgia syndrome disease was genetically engineered. This revelation, acknowledged by the Food and Drug Administration in a statement issued Aug. 23, raises the question of what role, if any, genetic engineering played in the toxicity of L-tryptophan food supplements.

According to the FDA statement, genetic engineering has not proved to be the "key causative factor behind the epidemic." On the other hand, casual involvement of genetic manipulation has not been ruled out.

On Aug. 9 scientists reported in the New England Journal of Medicine that 29 of 30 cases of EMS were traced to the product of one Japanese chemical company, Showa Denko K.K., and further that the cases were associated with batches of food supplement produced after Showa Denko introduced a new strain of fermentation bacteria, Strain V, now known to be genetically engineered.

The study further demonstrated that the toxic batches of tryptophan contained at least one new constituent, under study by the Center for Disease Control.

While these observations in no way prove that the genetic manipulations played a casual role in the toxicity of the disease-causing food supplements, they do leave open that possibility.

If we are to understand and avoid the risks presented by genetic engineering, it is important that any role genetic manipulation may have played in this tragedy be fully elucidated. MARGARET MELLON Director, National Biotechnology Policy Center National Wildlife Federation Washington