TWO prominent Chinese dissidents in exile have been invited to Hong Kong for the June 4 anniversary activities this year. But it is not yet certain whether they will be issued visas. This is despite many visits to Hong Kong by one of them, Liu Binyan, before the Tiananmen Square crackdown, and a brief visit immediately afterwards. The University of Democracy, a support group formed after the crackdown, has also invited Ruan Ming, former secretary to the late party boss Hu Yaobang. Mr Liu, 67, a former reporter with the People's Daily, was kicked out of the Chinese Communist Party in January 1987. He left China in March 1988 to take up a Nieman Fellowship in Journalism at Harvard University. Later branded a ''traitor to the nation'' for advocating sanctions against China, Mr Liu is apparently on China's wanted list. Vowing to return to China, Mr Liu said that he would only do so if China allowed him to remain free. He and Mr Ruan are in exile in the United States. Mak Lok-sun, chairman of the standing committee of the University of Democracy, said he could sense nervousness on China's side as the anniversary drew near. Mr Mak believed that China would not conspicuously exert pressure to bar the entry of Mr Liu and Mr Ruan. This was because former Tiananmen Square student leader Zhou Yongjun, after nearly a year in exile in the US, was allowed to visit Hong Kong last month. ''It is a sensitive time, and we would wait until the visas are issued before we start with the publicity,'' Mr Mak said. Mr Liu and Mr Ruan would be speakers at a seminar to be held on June 4. The University of Democracy is also organising an art exhibition, called ''Tiananmen Square - Yesterday and Today'' to commemorate the anniversary. ''These are mourning instead of commemorating activities. This year we want to look back and also ahead. We want to discuss what is the appropriate attitude to adopt [towards China],'' Mr Mak said. Meanwhile, the Hong Kong Alliance in Support of Patriotic Democratic Movement in China is also organising a series of activities for the anniversary. The programme will kick off on Sunday with the flying of kites and ends with the usual candlelight vigil at Victoria Park. The number of participants has dwindled, but alliance spokesman Cheung Man-kwong said this was the ''law of mass movements''.