DR. SEUSS & MR. GEISEL by Judith & Neil Morgan (Da Capo: $14.95, 346 pp., illustrated). Theodor Seuss Geisel almost single-handedly revolutionized 20th century children's literature with the Cat in the Hat, Horton, the Grinch et al. Drawing on interviews, letters and unpublished works, the Morgans offer an affectionate portrait of a shy perfectionist who often despaired while his books were in progress. Although the authors do their best to cover Geisel's life and achievements, the reader is left wanting to know more of his thoughts about his work. This biography is best read in conjunction with the recent "Dr. Seuss From Then to Now" and "The Secret Art of Dr. Seuss."