IF John Denver has ambitions to become a politician, perhaps he had better think again. Six-month-old Kwok Chi-weu (pictured with the singer) was not impressed yesterday when Denver tried a spot of baby-kissing - an art at which politicians must be expert. The 50-year-old singer, in town to play two concerts, picked on Chi-weu after planting a banyan tree in Wan Chai. Three years ago he founded ''Plant-it-2000'', a trust which has the objective of planting more than a million trees by the year 2000. For every T-shirt and souvenir sold at Denver's concerts, money goes towards this foundation. ''The important thing is we all work together to create a healthy environment,'' Denver said. ''We're all a global family.'' ''What do you think of the environment in Hong Kong?'' one reporter asked, as the Wan Chai traffic roared by. Squinting up at the tower blocks, and showing a better grasp of the politician's art than earlier, Denver said: ''Well, it's pretty crowded. But Hong Kong's lucky with its wind. There's not too much pollution here.''