Two sensitive tales about growing up. For preteens

Mark Makes His Move, by Marian Potter. New York: William Morrow & Co. 192 pp. $10.25. Ages 9-12. Rhoda, Straight and True, by Roni Schotter. New York: Lothrop Lee & Shepard. 160 pp. $10.25. Ages 9-12. TO know Mark Frye is to love him. The teen-age character of ``Mark Makes His Move'' hates swim lessons, shirks chores, and sells his sister's beloved stuffed animal collection at a garage sale. His intentions, however, are never mean or selfish. In fact, Mark loves his family, helps them improve their self-esteem, and becomes the town hero by saving an older woman's schoolhouse home from demolition by land developers. Mark is sensitive to his mother's plight as she faces the reality that soon her family will be grown and gone from the nest. He is also hardworking and thoughtful. To have a life with meaning, he takes the advice to ``treat family like company and company like family.''

This fully realized story of a boy's growing up is beautifully written. Marian Potter creates a believable working-class family of good but not goody-goody people. The woodland setting and town seem real.

In a counterpoint story within the book, Mark creates a fantasy world in which he and a tribe of imaginary Zanzutus are the only human beings left on earth. His task is to instruct them. Almost daily, Mark is the victim of bullies, but in his Zanzutu world, no one fights.

When Mark finally finds his identity as ``a kid of the late 20th century'' who has ``a lot of gumption,'' he realizes that he could not, even if he took a lifetime, describe to the Zanzutus ``all the world's wonders.'' He decides to leave the Zanzutus behind and work at things he can handle.

In Rhoda, Straight and True, Rhoda and her girlfriends occupy that cozy but narrow world in which young people strive to look, act, and think alike. Anyone different is ridiculed.

Rhoda goes along with this peer pressure until she is attracted to a classmate named Fig, a girl shunned because she is not middle class. Fig wears castoff clothes and she and her 12 brothers and sisters live with their mother in a shabby home, without enough water or food. When Fig offers a token of friendship -- a sprig of flowers -- Rhoda lacks the strength of character to withstand her girlfriends' taunts. In a cruel gesture, she throws the flowers into a wastebasket.

The friendship between Rhoda and Fig blossoms, however, as Rhoda learns to value persons, not appearances. She also learns to trust her own feelings, even if it means going against the crowd.

The setting for this important contemporary theme is 1953, when Americans were charmed by cowboy movies starring John Wayne and swimming-pool movies starring Esther Williams -- but alarmed by the Korean war. Spies, it was believed, were everywhere, and Rhoda, caught up in these suspicions, has to learn the hard way not to judge people who are merely ``different.''

Young readers should learn much from the faint glimpses of this troubling era. In fact, Rhoda and her girlfriends seemed very real to my 12-year-old granddaughter Autumn, and it was hard for her to believe the story took place in 1953.

``It's still true today,'' she said about peer pressure.

The writing here is smooth, though marred by exaggeration. The names of the 13 children are also a bit bizarre, especially the child named Delast (he was to have been ``the last''). Other extremes in the plot hint at a slightly patronizing attitude toward what was intended to be noble -- an understanding of poverty -- but the author's effort deserves applause.