LEGISLATORS and the Government are heading for a showdown over the proposed programme for British Dependent Territory Citizen (BDTC) passport holders to switch to British National Overseas (BNO) passports before 1997. After futile attempts to persuade the Government to halt the programme, legislators decided to take their grievances to the Governor, Mr Chris Patten, on his return from Washington. Convenor of the sub-committee on nationality, Miss Emily Lau Wai-hing, said members would also consider sending a delegation to lobby British MPs to reject the scheme. The Executive Council decided on Tuesday to press ahead with the compulsory exchange of BDTC passports to BNO. The implementation of the scheme, which requires people of different age groups to apply for the BNO passports before a set deadline between now and the end of 1996, is expected to begin in September. In winding up yesterday's heated debate of more than two hours, the Acting Secretary for Security, Mr Kent Woodhouse, said he was disappointed by legislators' comments. He claimed that the delay and confusion caused by members would make BNO passports applicants suffer, and said the scheme was not intended to keep people out. Mr Andrew Wong Wang-fat said legislators had no wish to make people suffer. ''We agree a phased programme will help orderly application for the BNOs, but we regret that the Exco had made the decision behind our back. ''The Government has insisted on their original position, but we should also speak for those who would like to retain their BDTCs until 1997,'' he said. Miss Lau argued: ''We are now being placed against the interests of the public, but what we are trying to do is to find means and ways to make the scheme more palatable.'' Some members suggested a trial run of the programme should by conducted, but this was dismissed by Mr Woodhouse. He also said the publicity campaign to inform people of the need to apply for BNOs will start this month. Sources stressed that there was no difference between the BNO and the BDTC passports. Out of 72 countries, Austria is the only country which still does not accept visa-free entry by BNO passport holders.