RADIO 4 is breaking away from its formal and rather dusty image in an effort to make classical music more popular. From the beginning of next month, the RTHK channel will try to follow the runaway success of Britain's one-year-old Classic FM station by adopting a lighter approach to what it calls ''fine music'' programming. As an RTHK spokesman said, Radio 4 will be shrugging off the dinner jackets and evening frocks, and slipping into something a little more comfortable. ''In a way it will be more like a pop channel - more informal and personal,'' said head of Radio 4, Richard Tsang Yip-fat. Mr Tsang said a detailed audience survey last April showed most listeners wanted a more lively and down-to-earth presentation of classical music. ''At the moment we are a bit pompous,'' he admitted. ''The announcers are given a schedule and everything has to be worked out before it goes on air: so there's not much creativity or commitment. ''There will be more job satisfaction with the new format,'' Mr Tsang said. ''As far as we are concerned we have been delaying a change long enough.'' It's bad news for some of the freelance announcers and interviewers who have been supporting RTHK's activities up to now: the anonymous ''continuity announcers'' that have been the acceptable voice of most classical music presentation since the beginningof radio are now counting off their last days at Radio 4. All programmes will now have a regular host, from Good Morning on Four to be presented by the new team of Jonathan Douglas and Vanessa Li, right through to the late night music programmes. Amy Kwong's Popular Classics programme has been moved to a more prime-time spot, and listeners throughout the day and night will be treated to more audience requests. Jazz will be back after a two-year absence, with Four and More on Sunday nights presented by veteran broadcaster and one-time professional bass player, Chris Hilton. And a new ''drive-time'' show called Art Beat, presented by Karina Zabini and Liz Case from 4 pm to 6 pm on weekdays, will combine music, features and interviews. ''I don't think there will be too many complaints that we have gone down-market, or that we have sold out to improve our listening figures,'' Mr Tsang said. ''We will still continue with our formal evening concert programmes. But because people want their music to be more approachable we are also trying to introduce new ideas into that area as well. ''For example, if we broadcast a concert live from Hong Kong, we will try to make it more lively by interviewing the conductor or the soloist during the interval to give an inside view on the music and the performance,'' he said.