World Can’t Get Enough of Princess Di : Royalty: A media frenzy pushes three books into the bestseller ranks. Says one palace watcher of the consuming interest: “I can’t explain it.”

Princess Grace had it. Princess Stephanie lost it. Prince Philip wishes he had it, and the current champ, Princess Diana, has such a corner on it that if Buckingham Palace loosened the leash a bit, she too could launch her own line of perfume.

The commodity in question: the ineffable ability of royals to rivet the public eye.

And now Diana, the Face That Launches a Thousand Magazine Cover Stories, has invaded book publishing as well, occupying three spots on the New York Times bestseller list. Andrew Morton’s “Diana: Her True Story” debuted at No. 1 on July 5, and has remained untouched since then; Nicholas Davies’ “Diana: A Princess and Her Troubled Marriage” is 8; and Lady Colin Campbell’s “Diana in Private” rests at No. 10.

Although not unprecedented--Queen Elizabeth and Princess Grace have had their share of the royal limelight--the phenomenon of three simultaneous bestsellers on the same royal topic has made the publishing world sit up and take notice.

Daisy Maryles, executive editor of Publisher’s Weekly, explains the hypnotic effect that the books--which detail Diana’s alleged marital woes, depression and suicide attempts--exert over readers: “It’s the ultimate dream fantasy gone wrong.”

Davies says the level of interest in the United States shocked even him, especially the reaction “among women, who I believe find it the greatest soap opera they have ever seen, because it’s real life.”

It is also a soap opera of the Electronic Age. During the Gulf War, the power of instant satellite communication brought us live missile attacks and stirred patriotic fervor. In the War of the Royals, the global media fed off of and amplified each other in a way that sent the public--on both sides of the Atlantic--slavering after fresh gossip.

Although other royals throughout the years have provided fodder for the gossip and news pages--King Edward abdicates the throne for Mrs. Simpson, Grace Kelly abdicates her seat among Hollywood royalty for Prince Rainier--no one has commanded the level of continuing fascination that Di has.

The first spark flew when Morton’s book was excerpted in the June 7 London Sunday Times. Highlights (five suicide attempts) were immediately picked up by the wire services.

Then, the release of Lady Colin Campbell’s book, originally set for September, was moved up to May to beat Morton’s book out of the gate, while Birch Lane Press, which had planned to release Davies’ book in July, rushed “Diana: A Princess and Her Troubled Marriage” into print a month early to cash in on the heightened interest.

“People literally worked 24 hours a day to get the stuff to the printer,” says Birch Lane spokesman Ben Petrone.

In the tabs, more than the usual amount space was devoted to the palace doings: the National Enquirer excerpted Davies’ book, and the Star, which had earlier excerpted Lady Colin Campbell’s book, ran a total of four cover stories on the unfolding palace scandal.

Meanwhile, back at the hardcovers, competition between the authors grew ugly earlier this month, when all three taped a segment of the Sally Jessy Raphael show that aired last month. “The fur flew,” says one audience member. “It was a blood bath.”

At one point, Campbell, trying to get a word in edgewise, turned to the monitor to face Morton and British gossip columnist James Whitaker, who were being beamed in via satellite from London, and said, “Shut up, you worms!”

During a commercial break, Morton reportedly sputtered that he was being lynched, while Davies tried to restore the illusion of civility.

To separate Davies’ book from the other two, Birch Lane ran an ad in the New York Times boasting that they offered readers a fatter book and therefore, more gossip. They compared Davies’ 359-page book (6 cents per page) to Morton’s 161-page tome (14 cents per page). “More Diana For Your Dollar,” the headline read.

For its part, St. Martin’s Press distributed a letter on Buckingham Palace letterhead noting that Campbell’s book was “uncannily accurate.”

Why Diana, more than any other royal, can stir passions so is somewhat mysterious even to professional palace watchers. Princesses Stephanie and Caroline, for example, are royal, glamorous and get themselves into as many--if not more--scrapes as their British counterparts. And yet the Monaco royals “are not in the same ballpark,” says Dick Kaplan, editor of the Star.

After a tumultuous youth that included a brief marriage to an older French playboy, Caroline has captured some of the dignity of her mother, notes Dan Schwartz, editor of the National Enquirer, but “Stephanie, I think, sleazed her image up to the point where people don’t really care.”

Even in the United States, royalty surrogates have a hard time competing with Di.

“Show me a magazine (these days) that can sell with Madonna on the cover,” challenges Kaplan. “Except for maybe a Rolling Stone, Madonna does not sell. She does much to be unlikable. People don’t like her penchant for taking off her clothes in public; they don’t like her attitude. She may be a billionaire, but all I can testify to is that she is not a cover name.

“I can’t explain it,” he adds. “All I can tell you is that Princess Diana is the leader of the pack.”

Publisher Steven Schragis, whose Carol Publishing Group owns Birch Lane Press, says that until “Diana in Private,” the most successful book he had published was 1989’s “A Woman Named Jackie”--a tell-all about the former Queen of Camelot--which spent 22 weeks on the bestseller list.

“The hardcover book-buying public is exactly the public that matches this subject: women more than men, women with time on their hands, older rather than younger,” Schragis says, noting, “There are very few people where there’s a total fascination about what they do.” The only other celeb who sells as well as Diana, he adds, “is the person we’re doing next, Elizabeth Taylor.”

In Britain, palace watching has become so competitive that every single one of the country’s 22 national newspapers has at least one correspondent devoted solely to royals coverage, says John Hannah, an editor for the British news agency Rex Features Ltd. Because they are so private, any information pertaining to the Windsors is highly valued. According to Hannah, Diana alone is worth close to $1 million a year to the agency in sales of stories and photos.

By contrast, there are few reporters assigned to cover only the Monaco royals. “That would come under the heading of the society beat,” Hannah explains.

Although each week seems to bring a fresh torrent of Diana stories and at least one TV movie is in the planning stages, Davies believes the fanatic interest in her will inevitably wane.

“To be brutally honest, I do not think they’re going to have the same interest in a 50-year-old Diana as they do in a 30-year-old Diana,” he says. “It happens to us all.”

Schwartz takes an even longer view. Having covered two, going on three generations of royal shenanigans, he sighs, “I imagine in a few years Caroline’s three children, and (princes) Harry and William cavorting in nightclubs, getting drunk, falling off ships and impregnating girls. It’s going to happen, you know. The royal line continues.”