THE Government has been forced to reconsider the terms for Hongkong's ''ambassador'' to the United States following revelations that the man designated for the job - Mr Barrie Wiggham - could immediately collect a $5 million cash pension payment. Conservative and liberal legislators yesterday united to challenge plans to make the Hongkong Commissioner for Economic and Trade Affairs a departmental post instead of an administrative officer grade job. The proposal would allow veteran civil servant Mr Wiggham to retire and collect a one-off pension payment before flying to Washington to take up his new post. Traditionally, the top job in Hongkong's overseas offices is an administrative officer post, but the current proposal envisages the Washington post, pitched at D8 grade on the directorate pay scale, as a departmental level job. While a D8 post is only taken up by policy secretaries who are administrative officers, officials argue that departmentalising the post will in the long run ensure that the Government can select the most suitable person, either an administrative officer or someone outside the administrative officer grade. Yesterday's special briefing was arranged for officials to explain the post's details. Mr Wiggham will head the Government's offices in North America at a cost of about $4 million a year. The Government also wants to buy a $20 million house for the commissioner. Explaining the Government's case, the Secretary for Trade and Industry, Mr Brian Chau Tak-hay, promised to reconsider the plan to departmentalise the post before seeking funding from legislators next month. ''If legislators cannot accept our rationale behind the plan, we can reconsider,'' he said. ''The most important point is to create a new D8 post.'' But Liberal Party preparatory committee convenor Mr Allen Lee Peng-fei said there was no reason for the move when the corresponding post at the London office was an administrative officer grade job. ''I am not convinced by the Government's explanation. Why shouldn't we make it an administrative officer grade post?'' he asked. Under present rules, an administrative officer grade post can only be held by a civil servant, while a departmental post allows the Government to recruit people from outside the civil service, including retired civil servants. Mr Wiggham, an administrative officer, could therefore retire from the civil service, before taking up the US job on a contractual basis, said Mr Chau. The Deputy Secretary for the Civil Service, Mr Michael Stone, confirmed to legislators that Mr Wiggham, 56, had opted for the new pension scheme and could collect half his pension as a one-off payment. Mr Stone said that Mr Wiggham, with 31 years' service, would receive a lump sum of about $5 million if he retired now.