SENIOR science students are worried they will get poor examination results in computer studies because essential study material had come too late to be of much use. Students taking the Advanced-level (A-level) Computer Studies and the first Advanced Supplementary-level (AS-level) have been badly affected by the late arrival of software packages from the Education Department. They have also complained about changes made in the computer language, compiler and network to be used in the exam. A Form Seven student recently wrote to Young Post saying he felt ''insecure'' because a much needed software package arrived late, and that his class had been waiting for it ''since Form Six''. ''This is a problem students of other schools suffer too. I plead with the Education Department to arrange everything before starting any new course,'' he wrote. ''Students need time to revise and prepare for the examination.'' Mr Lam Bon-cuong, a computer studies teacher at Po Leung Kuk Yao Ling Sun College, said his school did not receive the full set of software packages until last month, although the school introduced the computer class in 1992. ''Our original plan was to spread the computer syllabus over Form Six and the first term of Form Seven, and leave the second term for the school mock exam and home revision,'' Mr Lam said. ''But the plan was ruined because the department didn't send all the teaching material in time. ''The 'Prolog' package came only recently, just before the mock exam. Instead of going home for revision after the mock exams, students may have to come back to learn new stuff if the department decides to install a new network.'' The teacher said the department had promised to install a computer network so that schools could use the department's database and other resources, but this had not yet been done. Mr Lam took a three-day course offered by the Education Department in order to learn how to use the network. But the course proved ''useless'' after the department dropped the ''Lan Manager'' for the ''Novell'' system. ''I had to take another three-day course,'' he said. ''And now we aren't even sure if the department will install 'Novell'. We have heard that another system, 'Windows NT', may be used instead. That would mean another three days learning that network.'' Mr Teng Shiu-bong, the Education Department's principal inspector (computer education), said all software packages should have reached schools in time. ''But some special software may not be available in Hong Kong, and overseas orders would have had to be made. ''Besides, it takes time to look for suitable tenders. We have to talk to other government departments before going through public auction,'' he said.