The Schomburg Center for Research in Black Culture plans to announce the papers' acquisition this week.
Angelou, 82, said she sought out the Harlem institution - a research unit of the New York Public Library - as a home for works that include notes for her acclaimed autobiography "I know Why the Caged Bird Sings" and the 1993 inaugural poem "On the Pulse of Morning."
Angelou said Tuesday that she revised the poem about 10 times before getting it right.
"I had to continue to go back for the melody of the language," she told The Associated Press in a telephone interview.
"People all over the world use words; (then) the writer comes along and has to use these most-in-use objects, put together a few nouns, pronouns, verbs, adjectives ... and pull them together and make them bounce, throw them against the wall and make people say, 'I never thought of it that way."'
The Schomburg Center said the poem's draft is in one of nearly 350 boxes containing personal and professional correspondence, drafts, handwritten manuscripts and fan mail. It said that it has barely skimmed the surface of the material and that processing it will take up to two years.
"This is the essence that covers her literary career," Schomburg director Howard Dodson said.
The deal was sealed after a two-year negotiation, said Dodson, who has known Angelou for 20 years. He declined to reveal the terms.
Deciding to put her collection at the Schomburg was a "no-brainer," Angelou said.
"It is the principal repository in the world of literature and affairs for, by and about African-Americans, in particular, and Africans anywhere in the diaspora."
Angelou, who has homes in Harlem and Winston-Salem, N.C., said her many scribbled drafts are proof of how she can agonize over her writing.
"I want to write so well that the reader is 20 pages in a book of mine before she knows she's reading," she said.
For example, a typewritten draft of "On the Pulse of Morning" shows that she changed "Welsh" to "Irish" in the line: "The Irish, the Rabbi, the Priest, the Sheikh."
Angelou is the author of 31 books of fiction, poetry, nonfiction and children's books, as well as a cookbook scheduled for release in December. She has won three Grammys for her spoken-word albums and was nominated for a Pulitzer Prize for her screenplay and score for the 1972 movie "Georgia, Georgia."
The collection contains manuscripts, typescript, proofs or galleys for a number of her published works, including "A Song Flung Up to Heaven" and "All God's Children"; correspondence with writers Marshall Davis, Mari Evans and Chester Himes; photographer Gordon Parks; and jazz singer Abbey Lincoln.
In a six-page letter written Nov. 20, 1970, Baldwin - the author of "Go Tell it on the Mountain" and "Native Son" who died in 1987 - begins with the salutation "Dear, dear Sister," and continues: "I didn't know how much I needed to hear from a solid, loving funky ... friend."
"This is a truly remarkable human being," Dodson said. "The life record that she's created, especially as a writer, is of great significance ... not only of the times, but as an understanding of ourselves as human beings."
In a July 11, 1964, letter, typed on letterhead from the University of Ghana, where she was teaching, Angelou told Malcolm X: "Malcolm, I'm sure that we have not hada leader like you since the dead days of Frederick Douglass."
Five years before the publication of "I Know Why the Caged Bird Sings," Malcolm X foretold her literary success.
"Your analysis of our peoples (sic) tendency to talk over the head of the masses in a language that is too far above and beyond them is certainly true. You can communicate because you have plenty of (soul) and you always keep your feet firmly rooted on the ground," he told her in a Jan. 15, 1965, letter.
In terms of scholarly relevance, Angelou said she hoped some of her papers would show that Martin Luther King Jr. and Malcolm X were "were not demigods."
"Both those men were good men, strong and courageous, but they were men," she said. "I hope that in my papers people will find evidence that some of the people they would like to sit on pedestals were just like them, and so each of us has the possibility of being effective in changing our world, even if it's just the world around us."
The Schomburg archive also contains the papers of Malcolm X; Nobel Peace Prize winner Ralph Bunche; singer Nat King Cole; "A Raisin in the Sun" playwright Lorraine Hansberry; and tennis great Arthur Ashe.