''Hooked on Classics II.'' Royal Philharmonic Orchestra with the Royal Choral Society, Louis Clark. RCA. AFL1-4373. ''Hooked on Swing 2'' Larry Elgart and his Manhattan Swing Orchestra. AFL1-4589. ''Turned-On Broadway'' Vol. II. Broadway Symphony Orchestra, Luther Henderson. RCA. AFL1-4512. This second generation of disco-ized medleys is very similar to the first in style and content. Only the names (of the songs) have been changed to prevent any innocent music from remaining untouched. For most true lovers of classical music, Broadway show tunes, and swing the people who put out these versions of these musical styles are an anathema, or at least they should be. Purists dislike the forced beat and the medley style that reduces this music to pure pop. The question is, who are these records intended for? Admittedly, it's a moot one, considering the popularity of these LPs. So popular are they that RCA has announced there will be a ''Hooked on Classics III'' album to be released next month. Grudgingly, we'll admit that in small increments, these albums are fun. They've called on qualified musical talents (The Broadway Symphony Orchestra for ''Broadway,'' Larry Elgart and his Manhattan Swing Orchestra for ''Swing 2,'' and the Royal Philharmonic Orchestra with the Royal Choral Society for ''Classics'') to produce the medleys. They are snappy sounding, and give a broader survey of the most recognizable music from selected areas than ever before thought physically possible. Some of the snipets can, in fact, be rather successful in their translation to pop, and can hint at what the original might have been like. But taken as a whole, these records are uncompromisingly tiresome. The thumping beat and the relentless march from tune to tune would make it impossible for any orchestra to give any feeling of style or proportion to this music. Of the three , I liked ''Classics'' the best - perhaps because of the rich sound made by the Royal Philharmonic. It's all harmless, but these recordings hardly represent good examples of classical, Broadway, swing . . . or disco. But if these records help generate further interest in music, they do deserve some credit.