Biographer Ralph Martin has previously chronicled, among others, the lives of the Duke and Duchess of Windsor and Jennie Jerome, Winston Churchill's mother. His latest work returns him to Britain for an unauthorized biography of Charles and Diana, published strategically at the time of the first visit to the United States next week of the Prince of Wales and his wife. The book's jacket is symbolic of its contents -- handsomely designed, with glitzy gold lettering, and featuring a misty photograph of the beautiful couple rubbing noses on the dance floor.

The book, a curious mixture of sentiment and canned history, reads at times like a modern romance magazine. It also gives royal watchers some interesting tidbits to savor -- a sort of backstairs, upstairs and downstairs treatment all at once. The information does not seem very new or startling, but we are given a short, uncomplicated trot back through British history to set the scene for the many allusions to the monarchy. We're also given enough of Diana's heritage to conclude that she is no Cinderella; her family's own place in the British peerage is quite formidable.

The biographer gives us a breathless description of the meeting of the young couple, their engagement period, their wedding and the birth of their children.

Martin only touches on a major topic in England today: the relevance and the cost of the monarchy. He points out that it will be this young couple's challenge to convince their own young countrymen of the validity of their existence. Charles and Diana will increasingly face such critics as playwright John Osborne, who once referred to the royal family as "one gold filling in a mouthful of decay."

The young couple are portrayed as quite likable, particularly the prince, who seems to be a bright, dedicated fellow who takes his job seriously. The author should be forgiven for having relied on press articles, as well as interviews with sympathetic sources, for much of his information.

If he occasionally reveals a wart on the royal physiognomy (such as the fact that Charles is very sensitive about the bald spot on the top of his head), he also allows the prince a sense of humor. Charles, it seems, collects antique toilet seats. In his bachelor days, when he unveiled a portrait bust of his father at the stuffy Royal Thames Yacht Club, he announced, "I am not accustomed in any way to unveiling busts . . . I now complete the process of helping my father to expose himself."

Royal watchers will enjoy the trivia in the book, such as the "riveting" peek at some of the couple's wedding gifts:

" . . . fireplace bellows, two dozen champagne glasses, a dark green tablecloth, Royal Worcester china, a chicken fryer, two shocking pink lamps, two large beehive honey pots, a pair of Crown Staffordshire white cockatoos, a spice rack, six pairs of quilted table mats, a small George III mahogany three-tier what-not, two sun loungers with cushions, and a croquet set . . ." and so on.

The descriptions of life at Windsor and Balmoral castles are delightfully detailed, particularly the pomp and circumstance involved. Occasionally a royal family flaw is revealed, and it must be said the author does not document any intellectual abundance in the princess' makeup.

This royal watcher is puzzled that the author throws us a startling curve near the end of the book. After all the lovey-dovey stuff, he suddenly proclaims, "Despite their love for each other, it has not been a happy marriage. It has not been happy because the Princess -- from the beginning -- has never wanted to be part of the elite social scene of conversational banter, the glitter of royal state occasions, or even the center of the world's adulation."

Say not so, Princess Diana. Say not so!