THE British Ambassador to China, Sir Robin McLaren, said yesterday he hoped the ongoing Sino-British talks would reach agreement before he retired in August next year. The chief British negotiator, Sir Robin, 58, succeeded Sir Alan Donald, in May 1991 amid the Sino-British row over the airport. He will retire after a three-year term. ''I sincerely hope that these talks won't be going on in August next year. I am looking for a very early agreement,'' he said. Sir Robin also urged the Hongkong public to be patient and to accept that progress could only be made if the talks were confidential. Executive Councillors were yesterday briefed on the latest talks by the Secretary for Constitutional Affairs, Mr Michael Sze Cho-cheung. Mr Sze, the top aide to Sir Robin, will fly back to Beijing tomorrow with other supporting members of the British team for the fourth round of talks on Friday. Chinese sources said that during the third round of talks the two sides had come closer on the understanding of the provisions of the Joint Declaration, Basic Law and previous agreements reached. But the Chinese side had not yet put forward a whole package of concrete proposals for the 1994/95 elections. The source also said that the British side should stop using the question of the through train to block the normal proceedings. ''Otherwise, it would be difficult for the fourth round of talks to gain substantial progress,'' he said. In Hongkong, a vice-directorof the Hongkong branch of the New China News Agency, Mr Zhang Junsheng, said yesterday that the Sino-British talks were confidential. His remarks were made one day after Executive Councillor Sir William Purves was reported as saying that there was debate on the issue of through train during the talks. ''The contents of the talks are confidential. How can he learn about that?'' Mr Zhang queried. Asked if he felt that Sir William should know nothing about the talks, Mr Zhang said the question should be directed to the British side. Sir William was quoted as saying: ''Yes, there is debate on something called 'through train'. Let's wait to see what comes out of the talks. The good thing is that the two sides are talking.'' However, through the Exco press secretary, Sir William yesterday clarified that he was referring to the debate ''in the community''. The press secretary also pointed out that Sir William had declined to comment on the talks before making the through train remarks.