Fun with robots; Ready . . . Set . . . Robot! by Lillian and Phoebe Hoban, pictures by Lillian Hoban. New York: Harper & Row. 64 pp. $6.95. Your Very Own Robot, by R.A. Montgomery. Illustrated by Paul Granger. New York: Bantam Books. 54 pp. $6.95.

Given the success with youngsters of all ages of ''Star Wars'' and ''The Empire Strikes Back,'' and their personable droids, R2D2 and C3PO, it is not surprising that robots are also the key characters in two new children's books.

''Ready . . . Set . . . Robot!'' (An I Can Read Book) deals with the adventures of a robot type named Sol-1 in the galactic Dizi-Maze race. Though the setting may be out of this world, young readers will have no difficulty in identifying with a mechanical kid who needs to be reminded by Mama-Sol to clean his very messy space, and whose best friend is his mechanical dog, Big Rover. Drawings by Lillian Hoban add much to the story's appeal.

In the Choose Your Own Adventure series, ''Your Very Own Robot'' provides a variety of endings involving anything from vats of strawberry ice cream to pirates, with readers choosing from options at key points just how they want the story to continue. It's not exactly great literature, but the multitude of possible endings should provide several hours of enjoyment for a young reader. And the hardback binding (previous books in the series have been in paperback) provides more durability.