I AM surprised that there has not been more public debate surrounding the impending loss of a row of several large old banyan and other trees in Sports Road to make room for an extension to the Happy Valley racecourse. Bearing in mind the uproar concerning similar problems at Pacific Place and Stanley, it seems the Jockey Club development is proceeding free of criticism. I telephoned a few organisations whose approval, one assumes would be required. Buildings and Lands have not received a proposal as yet. The Urban Services has lodged a preliminary ''grievance'' but interestingly Environmental Protection and Agriculture and Fisheries Departments have no policy regarding trees. Not so Friends of the Earth whose policy is ''pragmatic and realistic'' as in ''you can't stop development''. This seems at odds with their indignation expressed over the solitary Stanley tree. Their spokesman also noted the Jockey Club's intention to plant 200 to 300 banyan trees to replace those destroyed. A clump of 300 fully grown banyan trees would be impressive viewing for those around in the 23rd century. It is my understanding that old banyan trees have considerable cultural significance to the Chinese community. I am sure I speak for many foreigners who appreciate and value all the remaining large trees in Hongkong and who hope that they can be preserved for everyone's enjoyment. DAVID SAYWELL Mid-Levels