BRITAIN will not sacrifice liberal legislators Mr Martin Lee Chu-ming and Mr Szeto Wah in exchange for an agreement on Hongkong's 1994/95 election arrangements, according to British sources last night. On the eve of another session of Sino-British negotiations on Hongkong's future constitution, they said Britain attached great importance to the so-called ''through train'' that allows legislators elected in 1995 to serve through 1997 in the first SAR administration. In what is seen as a British attempt to press for an early agreement on the electoral package, sources said they hoped China would come up with concrete proposals during discussions today and tomorrow at the Diaoyutai State Guest House's No 15 Villa. But there are signs that China may still want to concentrate on matters of principle. Despite three days of tough talking last week, the two sides remained divided on matters of principle, including whether the Governor, Mr Chris Patten's political reform package conformed with the 1984 Sino-British Joint Declaration, the Basic Law and previous agreements struck by London and Beijing. Sharp differences also remained on the ''through train'' issue, with China insisting on the right to veto legislators in 1997. However, sources close to the British team in Beijing said they could not sacrifice United Democrats Mr Lee and Mr Szeto for the sake of an agreement on continuity in the Legislative Council. Both Mr Lee and Mr Szeto were leaders of the Hongkong alliance which supported the pro-democracy movement in China in 1989 and the protests that followed the massacre around Tiananmen Square on June 4. They were branded as subversive and Chinese officials have repeatedly said both men would not be allowed to serve on the SAR Government. The source said that dumping the legislators would not conform with the principle of open and fair elections and the British also did not believe that such a move would be acceptable to the people of Hongkong. British team leader Sir Robin McLaren yesterday remained tight-lipped on today's talks. However, he also emphasised that the ''through train'' arrangements were extremely important. His remarks followed a signed commentary in the New China News Agency which said that existing problems and differences could only be solved if the two sides stuck to the principles of the Basic Law and Joint Declaration. Hongkong's Executive Councillors were yesterday briefed by officials attending the talks, including the Secretary for Constitutional Affairs, Mr Michael Sze Cho-cheung, on the progress. Speaking before leaving for Beijing, Mr Sze said he and his colleagues had an opportunity to report very fully to the Governor on what had happened in the first round of negotiations and discuss the second round of meetings. Following the second round of talks, it is expected there will be a two-week break before negotiations resume as Mr Jiang Enzhu, the Chinese negotiator, will be accompanying the Foreign Minister, Mr Qian Qichen, on a trip to Europe. The 12-day official visit will take in the Netherlands, Sweden, Italy and Germany from May 2 to 13. Mr Patten sets out on Friday on his trip to the United States. He will meet the President Mr Bill Clinton on Monday, his first day in Washington to lobby for an unconditional renewal of China's Most Favoured Nation (MFN) trading status. Meetings with Vice-President Mr Al Gore and Secretary of State Mr Warren Christopher are being arranged for the same day. Mr Patten's trip coincides with the introduction of a bill attaching conditions to China's MFN status in both houses of Congress. Mr Barrie Wiggham, who has been appointed Hongkong's ''ambassador'' to North America, is now in Boston, and will join the Governor to lobby for the MFN status. Meeting with Vice-president Mr Al Gore and Secretary of State Mr Warren Christopher are being arranged.