THE successful transplant of two banyan trees along Sports Road to the intersection of Wong Nai Chung Road will require the construction of a 10-metre wide steel-framed basin and a minimum 18-month period of root re-generation. Landscape consultant to the Royal Hongkong Jockey Club, Michael Kirkbride, said yesterday that the pace of the ''transplant should be as slow as possible'' for the 130-year-old trees, which have to be moved to allow the $741 million expansion of the club's facilities to proceed. A final decision on the fate of the trees, however, depends on Government approval of the Jockey Club extensions, delayed because of public support for the preservation of the banyans, and 49 less venerable trees. In January, the Jockey Club officials agreed that the trees could be saved but said that the process may be costly. Estimates later provided by consultants put the cost of relocating each tree at $1 million minimum. Consultant engineers are now about to grapple with the prospect of saving the trees; a process which requires the generation of a new root system for the concrete encased banyans before they can be re-planted in their new positions. The first step in the process is to begin severance of the root balls of the two trees from their mature root system assumed to have spread in a wider circle beneath the race course track and adjacent buildings. Steel sheeting will be placed around the trees and the tree surgeons will go to work to sever the mature tree roots. Each sub-system of the trees will be contained over a period of months within the steel sheet lining, until a new fibrous network of roots is established and the water-seeking system of the trees is again in balance. After the trees' cycles are stabilised, an area about 1.5 metres below the street surface of the trees will be excavated to complete the ''basin'' and allow construction of the transport scaffolding to begin. Professor Alun Griffiths of the University of Hongkong, who has prepared a report on the feasibility of transplanting the trees, said that the trees were very old and that a strong cage would have to be built to stop them from falling over while the rootsystems are being re-established. ''It will be a major, major piece of mechanical ingenuity,'' he said. If the trees survive this horticultural gamble, and there is not a territorial outcry about the narrowing of Sports Road during the process, the 60-tonne trees will be dragged 50 metres through shallow trenches to their new home where the Football Club now stands. Professor Griffiths said this week that he believed there was a 50-50 chance that the tree transplants would be a success. ''You have to realise that if a tree is 10 metres wide its roots radiate to possibly twice that distance in all directions from the base of the tree and it is only from the tips of the roots that the trees receive their water supply and nutrients. ''The normal process is to cut off one-third of the root system, at the base of the tree, and apply chemicals to stimulate growth and after six months or one year you have new feeder roots. Then you go to the next third and the final third. At the end oftwo years you have a new feeder root system as the rest of them will have died off. ''It's the first time it has been done on this scale in Hongkong. The trees are at least 100 years old. That is why I recommended in the report that the root replacement take place over 18 months, with another six to 12 months for the roots to properly regenerate.''