SO MANY BOOKS about sex have been published that you may feel that you've read it all before. But believe it or not, two new titles have money to say. The first, What you (Still) Don't Know About Male Sexuality, by Dr. Barry McCarthy of American University (Crowell, $8.95), is intended to supply a detailed overview of male sexuality as our notions of it change. It is refreshing to find a book which is sympathetic to the male sensibility in these matters, and McCarthy is aware that "today any sexual encouter that does not last at least thirty minutes and result in multiple orgasms for the woman might be considered an unhappy state of affairs, since the good doctor elsewhere notes that "Studies have shown that the average intercourse experience lasts only about two minutes, and the male argasm takes up only three to ten seconds of those two minutes."Vive la differece?

As for how the other half loves, there is Sex for Women, by Carmen Kerr (Grove Press, $10), billed as "the first feminist guidebook to sexual problem-solving." It is impossible to imagine a sexual subject not covered here, and persons squeamish about the very practical details of liberated sex would do well to avoid this volume. But if you are looking for very graphic answers to nearly unaskable questions, this is it.