EQUAL AFFECTIONS <i> by David Leavitt (Harper & Row: $8.95) </i>

An account of the strains the death of a domineering mother puts on the tangled relationships within an upper-middle-class American family. Nat Cooper, his children, April and Danny, and Danny’s lover, Walter, never achieve true equality of affection: Love must compete with boredom, resentment and unfilled desire in their hearts. Like the variables in a complex equation, their relative value shifts over time and distance. It’s interesting to follow those shifts in the work of this polished young writer, although “Equal Affections” lacks the immediacy that made “The Lost Language of Cranes” so compelling.