LEGISLATORS yesterday gave tacit approval to a government application for $940 million to build a tunnel for the airport railway alongside the West Kowloon Expressway, although construction of the airport rail link is still in doubt. Although there was no vote on the request, none of the legislators present objected. Convenor of the Legislative Council's ad hoc group on airport financing, Mr Stephen Cheong Kam-chuen, said the project was worthwhile as it would help ease traffic congestion along the Nathan Road corridor regardless of whether the airport railway went ahead. ''Even if there is no airport railway, the Government can still build a mass transit railway running from Hongkong Island to Tsing Yi to ease traffic congestion,'' he said after yesterday's meeting. Deputy Convenor, Mr Samuel Wong Ping-wai, said the cost of the line would be four times higher if it was built after the completion of the West Kowloon Expressway. The tunnel work would also be extremely disruptive after the expressway had been opened, he added. The related airport railway works include up to 920 metres of cut-and-cover tunnel to be constructed through the site of the Yau Ma Tei Interchange with the West Kowloon Expressway contracts. The construction sequence in this area requires the airport railway tunnel works to be completed before the start of construction of the interchange. The Mass Transit Railway Corporation will be asked to reimburse the Government for the cost of this work once financing of the airport railway is resolved. Although Britain and China have yet to reach agreement on financing for the new airport and its rail link, the Government said the construction schedule for the expressway was tight. Work will have to begin by the middle of this year if it is to be completed by 1996. The director of the New Airport Projects Co-ordination Office, Mr Gordon Siu Kwing-chue, said the airport alignment was in line with the Memorandum of Understanding on airport projects. The $940 million is part of a total funding request of $4.2 billion in money-of-the-day prices for the West Kowloon Expressway and linked roads. Together with a request of $886 million for installation of a traffic control and surveillance system for the Lantau Fixed Crossing and Route 3, it will be discussed at next Wednesday's Public Works sub-committee meeting before going to the January 29 Finance Committee meeting for final approval.