PLUNGING into Hongkong's often-polluted waters might become a less risky proposition under plans by one green group to offer a clean - and dry - tour of habitats under the sea. The World Wide Fund for Nature (WWF) is drawing up plans to build a marine education centre at Hoi Ha Wan near Sai Kung, where they hope to install a covered underwater walkway. Rather than simply reading about Hongkong's marine life, or looking at pictures of it, visitors will be able to watch first-hand the interplay of animals in one of Hongkong's few remaining underwater havens. Hoi Ha Wan is at the mouth of Tolo Harbour and its coral and fish have so far been spared the high pollution experienced deeper in the harbour, making it an excellent site for learning about marine life. Ms Jo Ruxton, WWF's marine conservation officer, said the group wanted to show people that Hongkong's waters were not only filled with sewage and industrial waste, and there was something worth saving from these hazards. ''One of the problems in Hongkong is the general lack of knowledge about the coastal environment,'' she said. ''A lot of people go to the beach and they don't know what's going on out there. But if something is pointed out to them, they become more interested, and if they are more interested they will be more concerned about what happens to it.'' But Ms Ruxton said the WWF has been pressing ahead with designing other attractions for the centre, such as special aquariums featuring marine animals and some of the more than 50 types of coral found in Hongkong waters. One tank will have daylight reversal, with bright lights on at night and infrared ones during the day, so people can view the hectic night-time underwater activity. Coral often feed in the dark, as do crabs and other creatures. Another tank will imitate tidal conditions to show visitors the mud-dwelling creatures that come out while the tide is low. A small research laboratory will also be in place so studies can be carried out, such as one by Hongkong University students to grow coral. The facility, expected to cost $12 million to $13 million without the underwater walkway, will be built over the water and stress education through films, talks, school tours and slide shows, similar to the centre at the WWF's Mai Po marshes reserve. The underwater walkway, which could cost another $7 million or $8 million, would be a first for the region. But its complex requirements mean the WWF will not be able to seek funds to build the centre until its design is complete. Taikoo Sugar, in the meantime, last week launched a project to raise money for the centre's educational programmes. Sugar packets are being sold in supermarkets with an illustration of a Hongkong marine animal on one side, and the logos of a corporate sponsor and WWF on the other. Companies pay $5,000 to display their logo on 50,000 sugar sachets. So far, four companies - Cathay Pacific, CityPlaza, Asea Brown Boveri and Modern Terminals Ltd - have between them paid $70,000. Ms Ruxton said they had hoped to have the centre built by the end of 1994, but that target was pending the completion of design plans. ''We really are working against time. The sooner we can get the centre up and running and the sooner we can protect this area, the better,'' she said. HONGKONG'S green groups usually do a commendable job of calling attention to environmental problems. But recently, and unusually, Friends of the Earth stretched the bounds of their mission too far. The group campaigned against the controversial and dangerous shipment of plutonium from France to Japan with less than honest tactics. While the shipment should be condemned, the group wrongly claimed during a protest in December that their action coincided with the ship ''passing by Hongkong''. The ship never came near the territory and instead passed through Australia and up the Pacific Ocean before arriving in Japan earlier this month - as Friends of the Earth was aware it would. It was fine for Friends of the Earth to draw attention to an issue meriting concern, but it should have based its tactics on fact. Otherwise people might stop listening. If your business or organisation has an environmental project of interest, or you wish to call attention to an environmental problem in your neighbourhood, please fax the information to Ecowatch, 811-1278, or mail it care of the South China Morning Post.