Biography fills gaps in our knowledge of poet Langston Hughes; Langston Hughes: Before and Beyond Harlem, by Faith Berry. Westport, Conn.: Lawrence Hill & Co. 376 pp. $14.95 in hard cover, $9.95 in paperback.

In this classic biography, Faith Berry examines the work of one of a few American poets who are read by more than the small poetry audience. Hughes's life is one that we love to read about in his poetry but which has not, until now, been commonly known. According to Berry, Hughes's experiences were representative of then-current black life styles, but the poems remaining in his books depict a less political poet and not the Hughes that commented with bitter humor on those times; Hughes apparently removed the more political work from currently available collections.

James Mercer Langston Hughes was born in Joplin, Mo., in 1907 to well-educated parents. His father, James Nathaniel Hughes, was an aspiring lawyer; his mother, Carrie Mercer Langston Hughes, a school teacher. Their relationship echoed an old story: Racism prevented James from attending law school, so he took a correspondence course and eventually left Joplin and the United States to become what he felt he could never be in America. Carrie, who was intelligent and cultured, worked for a while as a teacher but was eventually obliged to become a domestic - and a woman dependent on her son for emotional as well as financial support. James did achieve some material success abroad, but gave little to his son, and Langston grew up as a child needing, but deprived of , both parents.

He learned much, however, from his maternal grandmother, with whom he lived until he was 12, but his life with her was not a loving one. Among the things she taught him was ''the uselessness of crying about anything'' (though he did eventually mourn her death). She did, however, tell him stories of racial history, recounted from memory, and he would later recall her in a poem ''Aunt Sue's Stories'':

Aunt Sue has a head full of

stories.

Aunt Sue has a whole heart full of stories.

Summer nights on the front

porch

Aunt Sue cuddles a brown-

faced child to her bosom

And tells him stories.

(from ''Selected Poems'')

At Central High School in Cleveland, Langston celebrated the Russian Revolution with Eastern European and Russian immigrants - students whose families remembered living under the czar, to whom Lenin and Eugene V. Debs were important personalities. Poems such as ''Freedom's Plow'' and ''Migrant'' incorporate this experience. During a train trip to Mexico to see his father, Langston wrote on the back of an envelope perhaps his most famous poem, ''The Negro Speaks of Rivers.''

From Ms. Berry's skillful interpolations of the life with the work, we can see how Hughes's childhood, family, and times influenced his poetry. Seldom has a writer's life been shown as so integral to his work. Ms. Berry writes also of the Harlem Renaissance - Hughes's uneasy relationship with Zora Neale Hurston and the strange, exploitative use Ms. Hurston made of people.

In a discussion of Hughes's thoughts on Africa, Berry communicates his alienation from that continent as a world he could not quite call home: ''So long,/So far away/Is Africa.'' The poem concludes: ''So far away/Is Africa's/Dark face.''

After the Harlem Renaissance, Hughes mused, ''. . . how could a large and enthusiastic number of people be crazy about Negroes forever?''

After trips to Europe and Russia, Hughes returned home to Harlem, where he continued to write, although his work became more political. He directed it toward a black readership, with the creation of characters such as Simple, a sort of black Everyman and Negro spokesman.

One sees that Hughes was a poet in a way that Imamu A. Baraka, Nikki Giovanni , or even James Weldon Johnson could never be, even when his work was repressed because of his past associations with the Communists or by his interest in social causes. Berry also reveals that J. Edgar Hoover had a file on Hughes, and she explores the impact that made on his work.

Often 20th-century poets seem distant figures, absorbed in the craft of words and obscure meanings. But Hughes, perhaps more than any other American poet of our time, reflected the history, culture, and politics of a race of people through his own life and work.

Hughes's work grew out of the black heritage. This book reminds us that Hughes had already plowed the ground the black poets of the 1960s thought they had discovered. Hughes paid a price for his foresight and ended his life uncertain of what he had accomplished. In ''Langston Hughes,'' Faith Berry makes clear the monumentality of his accomplishment. Few writers have had better biographers.