NOTES ON BROADWAY by Al Kasha and Joel Hirschhorn (Contemporary: $22.95). As Oscar-winning songwriters, these two authors might have an exceptional appreciation for their peers' work. But as authors compiling interviews with the likes of Leonard Bernstein, Betty Comden and Adolph Green, Marvin Hamlisch, Burt Bacharach, Jerry Herman et al., they are in desperate need of a good editor. Introducing Jerry Bock, the commentator notes: "There are . . . two kinds of writers--those that love to write and those that love to have written." Another quibble: In entry after entry, Kasha and Hirschhorn seem to intend a book (not a show) called "Hair"; Bernstein gets singled out for his "bushy" stuff on top and, in a strange parallel, Bock's "curls" are coupled with his "wit." Once past the initial, idiosyncratic descriptions of their interview subjects, however, the authors go straight to the heart of the musical matter, eliciting candid comments from interviewees on their own contributions to the genre, as well as a general perspective on past and present Broadway--its inherent dilemmas and hopeful prospects. Bernstein, for instance, turns a typically analytic eye to what ails musical theater. In the process, he names Stephen Sondheim (inexplicably missing here) as the one important exception to a commercialism that rules the once-Great White Way.