WALDO is harder to miss than he is to find these days. Since his 1987 debut in the book "Where's Waldo?" the popularity of this bespectacled character has revolved around his elusive nature.But fans no longer have to scan detailed crowd scenes with several hundred figures in order to find Waldo in his trademark red-and-white striped shirt and hat. Where's Waldo now? Just about everywhere. CBS is airing a "Where's Waldo?" Saturday-morning cartoon featuring the character with his dog Woof. T-shirts, towels, and sheets sport the nerdy figure. He's even showing up on cereal boxes and in soap advertisements. Waldo's appeal is a bit of a mystery. Not even British illustrator Martin Handford, who created the character and has featured him in four best-selling books, can explain it. "Well, um, I really couldn't say," responds the author-illustrator when asked during a phone interview to explain Waldo's success. ve tried to make him a personable, likable character, amiable, well-meaning.... I would just guess that I've managed to ally him with something interesting like the crowd scenes that I do. I would imagine that without the crowd scenes, the character wouldn't have become as popular as he apparently has." Mr. Handford's unassuming nature keeps him a bit above the fray. But he can't help noticing that his four Waldo books have sold a staggering 13 million copies worldwide. A fifth book, "Where's Waldo? The Magnificent Poster Book!" has just been published by Little, Brown. Advance orders totaled 400,000, the largest preorder of any children's book ever published; the average for a children's book is 15,000. "Books that had pictures similar to the ones that I do were my favorite kind to look at when I was very young," Handford says. Although his works are billed as children's books, they clearly appeal to adults as well. Humorous elements such as a forklift hoisting a gigantic fork and a hippo getting his teeth brushed bring smiles to Waldo Watchers of all ages. It takes Handford about a month to complete each two-page spread for a book, and each page has at least 500 characters. Waldo books are published in 19 languages and 20 countries. But the character is known by a variety of names around the world. He's Wally in England, Walter in Germany, Charlie in France, Holger in Denmark, and Ubaldo in Italy. Meanwhile, others are hoping to reap the rewards of "Waldomania" through such imitations as "Hunt for Hector" and "Look for Lisa." A spinoff spoof, "Where's Dan Quayle?" was published by Collier Books last month. Although Handford lives modestly outside London and dislikes travel, Waldo's adventures often involve extensive globe-trotting. In "Where's Waldo?" he takes readers on a "world-wide hike" to such places as the airport, beach, ski slopes, and museum. "Find Waldo Now," Handford's second book, published in 1988, takes readers on a journey through time, starting with a cave-men scene and culminating with a peek into the future. In 1989, Handford presented "The Great Waldo Search," an exploration of fantasy lands ultimately taking readers to "the land of Waldos," in which a sea of Waldo impersonators camouflage the real Waldo, who is missing one shoe. "Where's Waldo? The Ultimate Fun Book," published in 1990, introduced the character of Wilma along with Woof the dog. Each book includes a checklist at the back, helping Waldo fans spot the many humorous elements included in each drawing. The artist admits to increasing the detail in each book, thus making it more and more difficult to pinpoint Waldo. "If one gets a buzz from this kind of thing, I think it's only fair to make it a little bit harder each time," Handford says. "I would hope that it makes it more fun." In fact, fun is the overriding purpose of these books, as far as the author-illustrator is concerned. The emphasis is on the pictures not the words. "There is a minimum of text quite purposely," Handford says. "I think my strengths lie as an illustrator, not as an author." A short, sassy paragraph introduces each spread, but from there it's a game of search-and-find. "I do believe that the nature of searching the pictures might encourage children to open up their minds in a general way," Handford says. "But I honestly couldn't say that I would expect them to look at one of my books and then move straight on to 'War and Peace' or something. It's a different kind of experience."