CASTLE KEEP by William Eastlake. 382 pages. Simon & Schuster. $5.95.
The castle stands deep within the Ardennes Forest, and in it dwells an aging nobleman who broods over his ancient lineage, his child-wife, and his priceless art collection. It is also occupied by the 314th Replacement Cadre, a foul-spoken band of American fighting boon-dogglers, including a cowboy, an Indian, a composer, a Negro intellectual, an art historian and an ex-preacher. The cadre is commanded by a sex-and-glory-hungry major. It is December 1944, the Germans are preparing to launch the Battle of the Bulge,...