Hearst Castle: San Simeon, by Thomas R. Aidala, photographs by Curtis Bruce. New York: Hudson Hills Press. 240 pp. $40.

The protean William Randolph Hearst drained the vast mining legacy left by his father and the wealth of his own publishing empire to build and furnish his hilltop castle at San Simeon. Today it looms over a secluded stretch of the Pacific coast, a fantastic and curious monument to the publisher's personal obsession.

The lively, thorough text and magnificent, haunting plates trace the 28-year collaboration between the capricious Hearst and his unflappable architect, Julia Morgan, who candidly remarked that the endless changes in plans required as much demolition as construction on the site.

The account is enriched by material from the Hearst family, and from friends as well as the publisher's builders, groundsmen, and gamekeepers. The castle, given to the State of California in 1957, still contains part of the uneven art collection Hearst assembled: ''silly, curious, and sublime works,'' paintings, statues, rare books, entire European rooms and halls, suits of armor, furniture, wellheads, doorways, window frames, and ''the ultimate folly,'' two entire Spanish monasteries, dismantled and shipped but never reassembled.