BRITISH officials have warned Beijing that time is running out if Hong Kong is to build the new military facilities demanded by the People's Liberation Army before 1997. In apparent recognition of this urgency, experts from the two sides have agreed to continue their talks on defence lands tomorrow. The marathon negotiating session, which began last Tuesday and is now set to become one of the longest ever, is a last-ditch attempt to reach an agreement in time to be ratified at the full session of the Joint Liaison Group (JLG). And one legislator warned last night the Legislative Council's views must be taken into account before an accord is struck. British officials have told their Chinese counterparts that speedy agreement is essential if the new military hospital and naval base on Stonecutters Island for the use of the post-1997 garrison, are to be completed before the change of sovereignty. Because of standard marine engineering practices, which stipulate precise time periods for reclamation work to allow deposits to settle, it would take about three years to complete the new naval base. This follows similar procedures used for the West Kowloon reclamation, which had to be left to settle for months before structural work could be carried out. There are already fears that aspects of the work on the base will run past the handover date but providing an agreement on military lands is reached soon, construction could get under way immediately. Some drilling has already been done around the proposed site to test soil samples but no heavy machinery has been moved there. Any accord is expected to include a tradeoff. China would allow most existing military sites to be turned over to commercial use, which could reap up to $100 billion in land sales, in return for upgrading other facilities for use after 1997. But the estimated billion-dollar cost of such improvements requires the approval of the Legislative Council's finance committee. If a deal is struck, the Government is expected to tell legislators it must be approved unamended before their July recess to enable the new facilities to be completed on time. United Democrats legislator James To Kun-sun called for the Legislative Council to be consulted. ''We have not been told anything about this deal so far,'' he said. ''The finance committee has the power to reject funding applications whenever they are inappropriate. So I hope the Government will act wisely this time, either consulting us before signing the agreement or specify the agreement is subject to appropriate funding being approved by the Legislative Council.'' Both sides refused to comment yesterday after a three-hour extended meeting on defence land. British leader Alan Paul would only describe the meeting as ''useful, pragmatic and in depth''. He declined to say if he was confident an agreement could be reached in time to be tabled at the full session of the JLG, expected to be held later this month or in early June. Britain is also discussing with China dates for a meeting of the JLG's airport committee, which is expected to be held within weeks. One Airport Consultative Committee member yesterday produced new figures which he said proved the row between the two sides could easily be resolved due to booming property prices. Francis Cheung King-fung estimated the income from property development associated with the airport railway project has risen to $120 billion, three times more than the original government estimate. This latest estimate is $20 billion more than the $100 billion figure government sources gave last week. Mr Cheung said by 1997, the Government would earn $72 billion from land sales along the railway. He suggested the Government inject half of this into the airport project, thereby lowering total debts associated with the project by $15 billion. In the Government's fourth financial package, recently put to the Chinese side, only $20 billion income from railway land sales would be put into the airport project. ''It will be much easier for two sides to reach an agreement under such conditions [of the new figures] since Beijing is always concerned about the debts,'' he said.