THE ice between the people of the mainland, Taiwan and Hong Kong recently thawed somewhat as leading musicians from the three countries came together to produce the theme song for a popular radio programme. Produced by Radio Television Hong Kong, the magazine-type radio programme, Putonghua Roundabout , has received positive reviews from listeners from all three countries since it first went to air on June 28. The show's target audience comprises Putonghua speakers in Hong Kong, new immigrants from China and visitors from Taiwan and South-east Asia. The theme song, called ''Words from Hearts'', was composed by Mr Kong Kong-sang, with lyrics written by Mr Lam Chik. It is sung by Taiwan's top male singer Dave Wang Chieh and popular mainland star Mao Yamin. Mao felt very happy about her first co-operation with Wong Chieh and the chance to help popularise the speaking of Putonghua. ''I think the best and quickest way to learn Putonghua is to listen frequently to Putonghua songs,'' Mao said. Wang said he was pleased to work with Mao, the top female artiste in the mainland: ''Apart from listening to Putonghua songs regularly, one should actively make friends with Putonghua speaking people.'' He explained that although learning Putonghua through songs might be an easy way, there could be some problem in the pronunciation of words, which differed slightly when used in everyday speech. Mr Cheung Man-sun, the Acting Head of Chinese Programme Services of RTHK, told Young Post he hoped the theme song would become popular in Hong Kong. ''A lot of people in Hong Kong are learning Putonghua through songs,'' he said. ''I think it is very effective.'' The programme's''Financial News of China'', which is relayed on Mondays, is the most popular segment due to the efforts of members of the Public Affairs Unit and the support of guest speakers from financial circles. Second in popularity is the song-dedication segment, called ''Thinking of You Tonight''. According to statistics, the majority of the listeners dedicating songs are Chinese immigrants in Hong Kong. Hong Kong's Putonghua beginners, visitors to Hong Kong, Shenzhen residents and Hongkongers who work in Shenzhen, come second. The two-hour radio programme is simulcast on weekdays from 8 pm to 10 pm on RTHK Radio 1 and 5. A number of scheduled outdoor activities will be broadcast live to give audiences more exposure to Putonghua.