The government must do more to preserve its internationally important tidal flats, domestic and foreign environmentalists said yesterday. At a news conference called by Wetlands International and the local environmental group Wetlands Alliance, Prof. Ko Chul-whan of Seoul National University proposed that the government designate all tidal flats on Korea's west coast as 'Ramsar sites.'' A Ramsar site refers to an area which meets the criteria of the 1971 Ramsar (an Iranian city)Convention on the protection of wetlands.