THE DIARY OF MORDEKHAI BEN-YOSEF by Benjamin Wolman (Schocken: $13.95). Not always filling 139 pages, "The Diary of Mordekhai Ben-Yosef" is the first novel (but by no means the first book) of Benjamin Wolman, editor of the International Encyclopedia of Psychiatry, Psychology, Psychoanalysis and Neurology. Set in northern Israel before, during and after the 1973 Yom Kippur war, the book depicts nine months in the life and puppy-lovelife of Mordekhai, who is 15 years old as he starts his diary and not much older when he stops. The book has its poignant moments--notebook-like horizontal lines at the beginning of each chapter give it the feel of a diary--but the author spends most of his waking moments agonizing over Miriam, who is also 15 years old and has promised to marry him and then thrown him overboard. Miriam's father is killed in the war, his own father is captured by the Syrians, but all Mordekhai worries about is Miriam's sneaky, daily visits to the house of an older man (he's an artist, she's a model). He fantasizes about the two, plots--with the help of an equally inept buddy--a ridiculous revenge and finally has a "man-to-man" talk with the artist to discern the truth. But, it is too late: Miriam is killed by Arab terrorists in the infamous Ma'alot school massacre. There's not much to either the hero or the book, but a young reader will learn about the tensions and hatreds that are part of life in the Middle East.