Maya Angelou's spare, hypnotic style brought the readers of her autobiography to the core of the blackness that shaped her girlhood, and that journey has been faithfully reconstructed in a two-hour movie tonight on CBS. "I Know Why The Caged Bird Sings," at 9 p.m. on Channel 9, brings honesty and warmth to the jumbled patterns of a girl's life, and leaves the viewer charmed.

The presentation is inmate, but in a time when sociology can overtake dialogue the filmmakers avoid preaching. A lyrical austerity underlines the performances, and Diahann Carroll, Rube Dee, Roger E. Mosely, Esther Rolle and Madge Sinclair-all veteran actors-contribute an authority and spare crispness to their characters.

The veterans are joined by two youngsters, Constance Good as Maya Angelous, and John M. Driver II as Bailey Jr., the brother Angelou adores. Angelou gets co-credit on the teleplay, and the dialogue has none of the trite predictability of many family dramas.

In "Caged Bird," Maya and Bailey are sent by their divorced parents to live in Stamps, Ark., where their paternal grandmother runs a grocery store. The gentleness of the rural town touches Maya's poetic instincts. Bailey coaches her on the defenses a poet and black woman needs-skepticism and pride. She learns slowly, automatically understanding the urgency and fear in her grandmother's voice when white vigilantes scour the countryside for black men.

Yet when her grandmother, played by Esther Rolle, seems to accept the degrading comments of three white girl,s, Maya screams, unable to bend to the protocol demanded by the South of the 1930s.

Each episode has its own beauty, as when neighbors crowd into the store to listen to Joe Louis' fights. Growing up, Maya and Bailey had been told their parents were dead. When suddenly they are not, the children react with shock, then a questioning bewilderment, followed by anger. They tear up toys and photographs sent by their new-found parents with such energy that no dialogue is needed.

Maya Angelou's growing years were full of ups and downs. The security and ease of Stamps is shattered when her father arrives to take the children to St. Louis, the home of their mother. Mother Vivian is a fast-talking, independent women who earns her money dancing and dealing cards. Bailey Jr. is immediately smitten and plans to stay.

In the role of the children's mother, Diahann Carroll handles the nervous, overly solicitous woman with an agility and realism that should redeem her from the doubters still smarting from her television debut as "Julia."

Life for Maya is totally darkened when she is raped by a boyfriend of her mother's. True to the spartan approach, all Maya says is, 'I'm hurt.'" Yet silence becomes her scar; when she can't be persuaded to talk anymore, her mother sends them back south.

Eventually, the drama ends on an upbeat note with Maya growing into a defiantly proud and sensitive teenager. A logical postscript would be for the sponsors to examine the wealth of the additional material Angelou has published and to give the rest the same balanced, thoughtful treatment.