A TAIWANESE opposition leader launched a bitter attack on President Mr Lee Teng-hui following the conclusion of the watershed summit in Singapore yesterday. Mr Shih Ming-teh, a leader of the Democratic Progressive Party (DPP), accused Mr Lee of ''betraying the interests of 20 million Taiwanese''. Mr Shih said: ''Now he [Lee] must say clearly what he means by unification. Does he really mean to turn Taiwan into a regional government under the People's Republic of China? ''If he really means this, then he must justify that by explaining to the 20 million Taiwanese that this is indeed their common wish.'' Mr Shih was in Singapore to observe the meeting between leaders from ARATS and Taiwan's SEF. And he called on the President to hold a referendum on ''Taiwan's national identity'' and to ''define and establish'' Taiwan's relationship with the mainland. In Hongkong, political commentators noted Mr Lee's more approachable policy towards the mainland, but said it was too early to say if there was a drastic change of stance on reunification. Chairman of Government and Public Administration at the Chinese University, Mr Tony Liao Kuang-sheng, said the talks marked the first step in a normal relationship. His view was shared by senior journalism lecturer at the Hongkong Baptist College, Dr Chen Yu-hsi, and the editor-in-chief of the Nineties, Mr Lee Yee. But Dr Chen said the issue of direct mail, communication, air and shipping links remained a big hurdle.