THE planned opening of the new Hyatt Regency Guam on October 1 hangs in the balance following the devastating earthquake which hit the western Pacific island on Sunday. According to a Hyatt Regency official, assessment of the hotel's condition was being carried out yesterday and the results will be known today. ''To date, we understand that the property, which is 85 per cent completed, was not affected in any major way,'' said Hyatt Hotels and Resorts official Letitia Law. ''Right now we don't know the exact state the hotel is in. I expect the hotel to open on schedule, but at the same time it all depends on the assessment,'' she said. She said a major problem at present was a loss of power as the earthquake had disrupted the island's electricity supply. While the chain is waiting for a decision on the Guam property, construction is continuing on a 406-room luxury hotel in Johor Baru in the Malaysian state of Johor. The US$50 million Hyatt Regency Johor Baru, being developed by JB Parade, a consortium comprising Yayasan Pelajaran Johor, Itochu Asia and Hong Leong Credit, is scheduled to open next year. Johor Baru is part of a growth triangle which comprise the state of Johor, Singapore and the Indonesian island of Batam. The state's proximity to Singapore and its natural resources have attracted huge local and foreign investment which is expected to reach M$10 billion (about HK$30 billion) in the next five years. Hyatt International senior vice-president for Asia-Pacific Larry Tchou said: ''The hotel's scheduled completion date of mid-1994 will be timely to accommodate an increase in both international and domestic traffic to Johor.'' In Surabaya, Hyatt Regency is in the final stages of completing its US$89.5 million expansion programme which will see the addition of 231 Regency Club rooms, 12 luxury serviced apartments and other rooms.