TOP hotel bosses are breathing easy over the plan for a huge new commercial complex in Causeway Bay. The 660-room landmark Lee Gardens Hotel is being pulled down and is likely to be replaced by a huge office and retail site. Now other luxury hotels are set to benefit from the business generated by the sudden loss of a competitor. And industry analysts do not believe they are under threat from developers looking for prime commercial land in the area. One analyst said: ''Causeway Bay is extremely attractive at the moment in terms of top quality office space. ''But the big hotels have nothing to worry about. ''I think the smaller, more dilapidated ones are vulnerable. ''Those situated in the right places could change hands soon.'' The Lee family announced the closure of the hotel with the loss of 750 jobs. It was bought by the Hysan Development Co for $2.45 billion, but was essentially an internal transaction because the Lee family are the single largest shareholders in Hysan. In what has been seen generally as a sound business move, Hysan has strengthened its already very strong hand in the Causeway Bay property market. Mr Gareth Williams, a director at leasing agents Vigers, said: ''Some people have done their figures and worked out that an office and retail building is going to give greater returns than a hotel. ''In the long-term this will be good for Hysan.'' According to Schroder Securities, 60 per cent of Hysan's 3.4 million square feet of investment portfolio is commercial property in Causeway Bay. It includes the Leighton Centre, AIA Plaza and Sunning Plaza. The $600-million Caroline Centre, a 31-storey office and retail complex, was officially opened in December last year. Another project, the redevelopment of the old Lee Theatre into a commercial complex, is due to be finished by 1994. Hysan is capitalising on the office space boom in Causeway Bay. More firms are moving there because top quality Grade A office space is available - and usually at 60 per cent of the rates in Central, where the limited supply has reduced new development to virtually nil. It is also popular with staff. There are plenty of shops, restaurants, entertainment and leisure facilities, and it is conveniently near the MTR station - the new Times Square towers have an entrance in the basement. ''It has become acceptable to set up in Causeway Bay,'' said Mr Craig Wallace of Colliers Jardine. But some agents have warned that the top office space will dry up inside a few years once the major new developments open for business. Ms Pauline Wong, Hysan's property director, agreed. She said her own firm's projects and Times Square were the last of the big projects. ''We see a lot of potential in this district. We are very positive about the property market in general. ''If you look ahead there may be some smaller activity but you don't see any big developments coming on stream,'' she said. Developers wanting to cash in on the district's potential may start looking at the sites of existing buildings. Mr Brian Oung, a research analyst at Sun Hung Kai Securities, claimed hotels wouldn't be swallowed up. The big luxury five stars were too well established, he said, and three and four star hotels were doing the best business. It would not be cost-efficient to tear them down and spend millions building offices. ''Lee Gardens is an exception. I don't think it will be repeated,'' he said. Excelsior Hotel general manager Mr Liam Lambert was not remotely worried about the future. He saw no threat from commercial developers. But he saw more office and retail complexes opening in the neighbourhood and more corporate clients going to his hotel. ''I think a lot of apartment buildings about 30-40 years old could be targeted,'' he said. ''In the next five years I feel hotels in this neighbourhood will do tremendously well. ''I would just like another 500 rooms, please.''