The author of such classics as My Granson Lew, Williams's Doll, and Over and Over needs no introduction. Neither does her collaborator Maurice Sendak, who has illustrated so many of today's best-loved, as well as most distinguised, books for children. The heroine of their book has a problem. And at first it does not look as though Mr. Rabbit is going to be much help in solving it . For everyone knows you cannot give your mother a red roof, a yellow taxi-cab, a green caterpillar, or a blue lake for her birthday. But then all the little girl had said was that her mother liked red, yellow, green and blue -- and so Mr. Rabbit was trying.How he and the liitle girl come up with the absolutely perfect present makes a story the the youngest reader will love. And the wonderously bright full-color pictures will bring hours of pleasure to readers and lookers of all ages