CHINA'S chief negotiator Jiang Enzhu may well begin the talks with a long opening statement outlining in great detail Beijing's principled position on the question of Hongkong's political future. Sir Robin McLaren will then rebut all the principles detailed by Mr Jiang one by one and suggest they move on to the matter at hand, namely working out the arrangements for the 1994-95 elections. Mr Jiang will reply that only by agreeing on the basic principles can the practical details be worked out. Sir Robin will say the two sides will just have to agree to differ on the question of principles and will then try to steer the talks back to the elections, saying the British side thinks it would be a ''good idea'' if they were held in this particular way. Mr Jiang will say that idea is ''totally unacceptable''. ''Why?'' Sir Robin will ask. ''You know why,'' Mr Jiang will counter with a look of satisfaction. The British team will then exchange looks of incomprehension and Sir Robin will say: ''Well, maybe we are a bit stupid but we really do not know why the Chinese side cannot accept this plan. Perhaps you would care to propose some ideas of your own.'' Mr Jiang will then throw his hands up in horror and say that is not the responsibility of the Chinese side. ''Why?'' Sir Robin will ask. ''You know why,'' Mr Jiang will reply, ''our principled position is well known. It is up to the British side to come up with a plan that is in accordance with the Sino-British joint declaration, the principle of convergence with the Basic Law and the relevant agreements and understandings reached between China and Britain.'' ''This is quite ridiculous,'' Sir Robin will say raising his voice just enough to register his displeasure, ''we could be here all year if that is your attitude.'' The two sides will then agree it is probably a good time for a recess. The next morning, Mr Jiang will suggest in a slightly offhand manner that if the British side were to suggest that the elections were held in a particular way, the Chinese side might be willing to discuss the matter further. The British side will then exchange meaningful glances and Sir Robin will say: ''That is totally unacceptable.'' ''However, we would be willing to agree on some points if you were to agree on certain points in our original proposal.'' Mr Jiang will hold whispered discussions with Mr Wang Fengchao and his other colleagues and say: ''I'll have to get back to you on that one.'' The two sides will then agree to conclude the talks and reconvene again in two weeks' time at a place to be disclosed.