BRITAIN and China are locked in a row over Hong Kong's air service agreements with foreign countries, casting uncertainty over whether there will be enough flights to maintain the new Chek Lap Kok airport. Negotiations have been dragging on - with one delayed by more than four years - because the flights involved are connected to Taiwan. China, which considers Taiwan as one of its provinces, argues that the Hong Kong Government has no right to come to an agreement with other countries on flights between Hong Kong and Taiwan. This is because, under the present international covenant on aviation, a foreign airline is not allowed to operate between two cities within a country. But at present, flights between the territory and some foreign countries - such as Singapore and Japan - include connecting flights to and from Taiwan. It is understood the Chinese side asked for details of the Taiwan flights involving seven countries as early as 1990. But the British side refused, arguing that the information contained commercial secrets involving a third country. China warned that discussions on the agreements would be held up unless they were given the information. The countries involved are Germany, Italy, Burma, Indonesia, South Korea, Singapore and Thailand. Chinese negotiators have insisted their request is ''reasonable and have taken into account the historical reality'' of the territory. ''The ball is in the British court,'' a source said. Under the Sino-British Joint Declaration and the Basic Law, any agreement between Hong Kong and foreign countries that involved flights or stopovers in other parts of the mainland has to be signed by the central Government. A source said the Chinese side was ready to maintain the present arrangements given the special circumstances of the territory. But it is understood that China wants to reserve the right to re-negotiate with countries which enjoy the right of transit flights to and from Taiwan. Another source claimed that the intention of the state-owned Civil Aviation Administration of China to fight for a bigger slice of the lucrative aviation business was the reason for the snag in negotiations. The source said the matter might also have been complicated by the dispute between China and Taiwan over the reunification issue. A British source warned that Hong Kong would suffer if the dispute dragged on. There would not be enough flights coming in and out of the new airport if the problem remained unresolved, he said. The British side has proposed that a meeting between experts be held on the agreements issue before the full Joint Liaison Group (JLG) session scheduled for the end of next month, it has been learned. At present, Hong Kong's agreements with foreign countries formed part of the relevant accords between Britain and those countries. Separate agreements will have to be made between the territory and other countries in the face of the sovereignty changeover. Eleven agreements have been approved by the JLG. They are the Netherlands, Switzerland, Canada, Brunei, France, New Zealand, Malaysia, Brazil, Sri Lanka, Australia and India. Except for India, all others have been signed.