Gift ideas -- choicest new books for the holidays; Disney's new 'Waltopia'; Walt Disney's Epcot: Creating the New World of Tomorrow, by Richard R. Beard. New York: Harry N. Abrams Inc. 239 pp. $35.

Writing and photographing a book about a place that Walt Disney said ''will never be completed'' can't be easy. This big picture book about the Epcot Center , Disney's dream-come-true, captures the ''Experimental Prototype City of Tomorrow'' as it was just before it opened last month. Colorful artists' conceptions give an idea of what many of the coming attractions will be like, while photos take the reader for a stroll behind the scenes at the $800 million theme park.

Although not the definitive discussion of Epcot, this official Disney version of the park's birth makes a good visitor's preview to what one Disney official has dubbed ''Waltopia.''