Two enjoyable choices for beginning readers; The Longest Float in the Parade, by Carol Carrick. New York: Greenwillow Books. 55 pp. $7.95.

Hush, Puppies, by Barbara Mitchell. Minneapolis: Carolrhoda Books. (241 First Avenue, N. 55401.) 47 pp. $6.95.

Writing an entertaining story in simple words is not an easy task. Children are quick to reject a book that appears to talk down to them. ''The Longest Float in the Parade'' is an easy-to-read story of summer camp rivalry that beginning readers are sure to enjoy. Assigned to make a group parade float, the boys want to be soldiers fighting a battle, but they are outvoted by Darleen and the other girls who want to dress up like queens and sing sweetly. The widely differing ideas create humorous developments, until Jimmy and Pinky dream up a float that appeals to everyone.

Donald Carrick's exuberant watercolor illustrations add yet more fun to the story.

Not quite so simply written, but with more lasting impact, is ''Hush, Puppies ,'' an engaging yarn about how those delicious fried corn meal balls got their name.

Based on a South Carolina low country legend, the plantations and people in the story are fictional, but the author has used historically authentic details to bring alive some of the unique contributions that African slaves made to America's heritage.

The black and white pictures by Cherie R. Wyman portray everyday slave life with dignity and understanding.