GIVE US THIS DAY (254 pp.)Sidney Stewart Norton ($3.50).
THE LAST PARALLEL (333 pp.)Martin Russ Rinehart ($3.95).
A soldier's courage has become a stranger and subtler virtue since the days when Spartan mothers clapped their sons off to the wars with the stark injunction: "Return with your shield or on it." In the jungle retreat of Bataan, it became necessary to resist in a seemingly lost cause. On the frostbitten ridges of Korea, it became necessary to carry a stalemate to its logical inconclusion. In these tragic endurance contests, new kinds of American courage...