Pick of the paperbacks; A Poetic Equation: Conversations between Nikki Giovanni and Margaret Walker. Washington, D.C.: Howard University Press. $5.95.

The two women who wrote this book could scarcely be more black. As poets and writers, they capsulize in these recorded conversations black American culture in the 20th century. What they say should not be ignored.

Their differences of opinion, which are many, show both a generational difference -- Mrs. Walker of the conservative '40s and '50s and Miss Giovanni of the impatient and militant '60s and '70s -- and the conflicting philosophies within black consciousness today. The book is most exciting when the women discuss literat ure, their own and others.