THE Education Department has revealed plans to set up a hotline for troubled youths. The news came as a Cantonese-language suicide-prevention hotline admitted to being overwhelmed by callers, and urged the Government and associations to set up more telephone help lines. ''A telephone line is being considered by the Education Department to receive phone calls from students who may have problems,'' said department spokesman Mr Richard Law Chi-ming. A decision is expected within the next few weeks. Meanwhile, Ms Joyce Chow Yuen-fun, vice-chairwoman of Samaritan Befrienders Hongkong, a 24-hour suicide-prevention hotline, has admitted that the service is facing a manpower problem and there may be times when the service's three lines were not manned. Although Samaritan Befrienders Hongkong does not target students, statistics show that during the first half of 1992 more than 21 per cent of new cases recorded were between 10 and 19 years old.