Real-life stories with quiet humor; This Strange New Feeling, by Julius Lester. New York: The Dial Press. 149 pp.

''He knew that the three children Jessie birthed didn't die because they were sickly. . . . She had smothered them babies with her own hands. . . . They didn't grow up to be slaves.''

It's passages like this that make ''This Strange New Feeling'' hard to forget.

As a meticulously researched account of life in America under slavery, this book should get high marks from teachers and school librarians. As a collection of believable, real-life stories, it has the kind of heroics and understated humor that older readers appreciate most.

In the title story, Ras, a muscled young field hand, gets his first taste for freedom listening to the stories told by a white laborer who's come south for the summer months. With the help of his Uncle Isaac and a sympathetic white plantation owner, Ras makes his way north to freedom wrapped inside a bale of cured tobacco leaves, returning later to help other slaves escape.

Then there's Maria, who marries a free black man and enjoys a few years living in the ''sun'' of freedom, only to be sold into slavery again to pay off his debts when he dies. Standing tall and proud to the very end, she warns the slave auctioneer who comes to take her that he won't need a rope to tie her. ''I ain't going to run away,'' she tells him because she knows now where the sun lives.

Finally there's the story of William Craft and his half-caste wife, Ellen, who elude their masters by traveling from Georgia to Massachusetts as a young white master and his submissive ''boy.'' Equally powerful in its depiction of the antislavery struggle and young love; this is the most moving of the three.

Newbery Honor Book author and National Book Award finalist Julius Lester has worked hard to produce the clean writing and free-flowing dialogue that bring these historical characters to life. We see fog, ''lying over the ground like scraps of cotton,'' and a blacksmith's legs, stretched ''like snakes sunning on a rock down by the creek.'' There are simple statements that say a lot: ''If they see us cry, then we won't have anything left that's ours.''

Not all the endings are happy ones. But, taken together, they should give freedom a tangible new definition.