A fairy godmother was wandering around the South Lawn of the White House yesterday afternoon, dressed in a long, light violet robe, carrying a silver wand and wearing a silver crown on her long, curly, snow-white hair.

"Are you the wicked witch of the west?" asked one of the 200 children who were guests at a party hosted by Amy Carter.

"Shut up," she murmured sweetly, "or I'll turn you into a toad."

There were no wicked witches in sight at the White House celebration of the nationwide "Reading Is Fun Day," but there were people costumed as a bear, a pirate, Mary Poppins, Pinocchio and Robin Hood, as well as such real-life notables as Rosalynn and Amy Carter, Carol Burnett, Arthur Ashe, John Chancellor and Maurice Sendak.

There were also a half-dozen mimes in white-face cavorting around the East Room and the South Lawn, shouting soundlessly at one another, playing tug-of-war with imaginary ropes and pointing invisible cameras at the press photographers who were pointing real cameras at them.

There were also the children, mostly from Washington, invited to come and munch cookies, browse books and launch balloons with the first family. Each of the balloons bore a tag reading: "my favorite book is -- --. What's yours?" And each asked the recipient of the balloon to write the launcher, whose name and school address were incribed on the tag.

Before the lawn party, there were more formal ceremonies indoors in the East Room, with Nbc's chancellor presiding, Amy Carter and Carol Burnett reading some of their favorite poems and Rosalynn Carter welcoming guests with the instruction that "this is an afternoon for fun."

"How many people here like to read?" asked the first lady, and the 200 tiny guests raised 200 tiny hands.

Out in the lobby, the Marine Band, which has something appropriate for every occasion, played excerpts from "Babes in Toyland."

Before introducing Amy, who read a poem called "The Voices of the Trees" by fifth-grader Mardi Strejack of the Key Elementary School, Chancellor noted that "the Carters are great readers . . . I understand they even read at table during meals.

"The first time I saw Amy Carter at a social function at the White House," he said, "she spent most of the time reading a book. I must admit that through the years there have been many White House functions at which I wished I had brought a book.""

The national sponsor of "sponsor of "Reading Is Fun Day" has a name that is almost identical with the day but a bit longer: Reading Is Fundamental Inc., a nonprofit organization whose goal is to bring children and books together. Yesterday, throughout the country, some 2 million children participated in programs like the one at the White House, picking out free books to read and keep as their own.

After the balloons were launched (including a half-dozen that got caught in trees) and the books picked over, a crowd of autograph-seekers gathered around Maurice Sendak, whose books had been among the first to disappear from the giveaway tables.

The crowd was headed by the two Carters, the mother introducing the daughter to Sendak as "a great fan." He autographed one of his "Reading Is Fun" posters "For Amy , with pleasure," and beside his signature he drew a picture of himself as a horned monster from "where the Wild Things Are," his most popular book and the basis for an opera which is nearing its world premiere.

The party broke up much like any schoolchildren's party. The last few guests called back over their shoulders, "'Bye, Amy -- see you later . . . call me," and drifted away like the message-bearing ballons floating out over the Washington area. One of those ballons had a tag fulttering on its string that was made out by Rosalynn Carter, gave her address as the White House and listed as her favorite book, "Why Not the Best?"