In a surprising defeat of a government-owned rail company, environmental officials in the heavily polluted destination spot known as Hong Kong refused a permit request last fall to build a passenger line across Hong Kong’s largest freshwater wetland. The Kowloon-Canton Railway Corp. has mounted an unprecedented appeal and spent loads of money to come up with new evidence that the route through the wetland would be environmentally a-okay. The case, which began last week, is the first to be heard by the Environmental Impact Assessment Appeal Board since an environmental impact law was enacted in 1998.