I should like to take exception the slant of the article "Busy Beaver Boom Is Wreaking Havoc," Sept. 26. The beaver is not only a superb architect but also a great little ecologist. Beavers dam up streams often preventing floods. I would not be surprised to learn that engineering - not a beaver dam - was at fault in the flood that closed the Trans-Canada Highway. Beavers may be better engineers than humans.Rhoda M. Crowell, Tilton, N.H. Letters are welcome. Only a selection can be published, subject to condensation, and none acknowledged. Please address them to "Readers Write," One Norway St., Boston, MA 02115.