Hooked on Swing. Larry Elgart and his Manhattan Swing Orchestra. RCA AFL1- 4343. Turned-On Broadway. Broadway Symphony Orchestra. RCA AFL1-4327. - Here are yet two more albums of music forced into the disco beat from the makers of ''Hooked on Classics.'' Remarkably, they are more fun than they are wearisome. Fortunately, both ''Turned-On Broadway'' and ''Hooked on Swing'' feature crack orchestras. Of course, what we've got here are two super-medley albums. There are 95 (count 'em, 95) tunes, for instance, on the ''Broadway'' one. And each tune's moment under the needle, so to speak, is no more than a few bars of the most remembered parts of the songs. Then, too, there's that disco clapping noise much of the time, in case you don't know when to tap your foot. This can become bothersome. Considering these constraints, these albums are quite listenable, although in small portions. They're not great music, but they succeed at what they try to do.