THE decision to appoint Mr Barrie Wiggham as Hongkong's ''ambassador'' to North America has won backing from the American Chamber of Commerce. Chairman Mr Lyn Edinger said it would be unfortunate if the Hongkong Government's proposal to upgrade the Economic and Trade Office in Washington was voted down by Legislative Councillors next month. The attempt to upgrade the post to secretary level and to appoint Mr Wiggham has been criticised by Legco members as a costly move to tailor-make a job for an expatriate. ''The appointment of Mr Wiggham is a very good idea and we think that this should not be a subject of such debate and concern,'' Mr Edinger said. ''I think it is a substantial statement, the sort of statement that Washington takes note of when a position for representation is substantially upgraded. ''The posting of the man who is currently the No 3 in the Government to Washington will be seen as a measure of [the] interest and commitment by the Government of Hongkong on how important they view the bilateral relationship. ''Mr Wiggham is a very accomplished diplomat. I think he'll be extremely effective in dealing with Washington. During his tenure, he'll get Hongkong's message across effectively at a very senior level,'' Mr Edinger said.