JFK JR., DIANA FOREVER IN PRIME.

Byline: Ted Anthony Associated Press 

Their easy smiles and their glamorous lifestyles catapulted them to an unparalleled upper tier of fame - a perch unusual even for this celebrity-obsessed nation. Somehow, these two were different.

She was an actual princess; he was the closest thing this country had to a prince. America's tragedy was his personal loss; her private trials became public obsessions.

``It kind of seems like Princess Diana all over again,'' said Melissa Monahan, 23, of Dumont, N.J., visiting the flower-festooned stoop outside John F. Kennedy Jr.'s lower Manhattan loft Sunday.

Diana and JFK Jr., whose superstar allure made them objects of desire, whose sorrows made them seem accessible, lived different lives under very different circumstances. Yet each of them - tragic young people who lived well and were lost abruptly - represents the pinnacle of enduring celebrity.

It's a 20th-century phenomenon, driven by movies, television and now cyberspace, born with the likes of Rudolph Valentino and Jean Harlow, refined with James Dean and Marilyn Monroe.

Hollywood created the star machine; then the rest of the world went Hollywood. During the tumult of the 1960s, Jack and Bobby Kennedy, Malcolm X and the Rev. Martin Luther King Jr. became a new kind of celebrity that blended achievement and allure. Their assassinations ensured it would last forever.

Not so for many young superstars, who tarnish with age. The corpulent Marlon Brando will never eclipse the forever lanky Dean, and Monroe has far more staying power than an Alzheimer's-stricken Rita Hayworth ever will.

Now JFK Jr. and Diana are frozen in that video-age amber, their legacy an archive's worth of images ready for eternal playback on TV and the Net, showing them forever in their prime, the ordinary and the extraordinary in one slick package.

``We're living in a time when the machines of mythology are more powerful and pervasive than ever,'' said Art Simon, author of ``Dangerous Knowledge: The JFK Assassination in Art and Film.''

Both Diana and JFK Jr. were easy sells, examples of historian Daniel J. Boorstin's 1961 definition of celebrity as ``someone known for their well-knownness.'' They sold well: Diana has been on the cover of People magazine 50 times, JFK Jr. 15.

The lovely Diana was the ideal royalty for a talk-show culture that demands accessibility with its pipe dreams. She was divorced. She fought bulimia. Her blemishes showed through the glitz but never overshadowed it. Her mother-in-law, the queen, traveled in limos; Diana kissed AIDS patients.

JFK Jr.'s very lineage ensured him a place. He was the namesake and most visible vestige of Camelot, of a time and a presidency that may not have been innocent but is remembered that way.

But while his parents were patricians who appealed to common folk, he was a self-styled commoner who, though a Kennedy, favored in-line skating around his neighborhood and throwing Frisbees around Central Park. Jackie Onassis might well sweep into the Four Seasons behind oversized sunglasses; her son favored breakfast at Bubby's, a corner restaurant in his Tribeca neighborhood. Like Diana, he stooped to conquer, and it was captivating.

``I was saying to myself, Why are you feeling like it was your loss? Why is it so painful?'' said Lavonne Smith, 43, of Chicago. ``That's the way it was with Princess Di - all weekend.''

Yes, people said, he was a celebrity, but so many likened him to a little brother or a son or a regular guy. He seemed the nation's property: They took his father away, people said, so he belonged to us. Much like the language that British and Americans alike used when Diana died.

``Most of the times that we see them, they're doing something that Joe American would do,'' said Matt Hogge, a 24-year-old chemical engineer from Pittsburgh.

Still, JFK Jr. was never one of us; he was the son of a mythic president just as 17-year-old Prince William is the son of a real princess who will spend his life living up to her memory. In an interview just before her death in an August 1997 car crash, Diana suggested the younger Kennedy's approach to fame might be a useful model for her son, a future king.

``I want William to be able to handle things as well as John does,'' she told The New Yorker.

Then she died and joined the ranks of the famous who never grow old, who become blank slates for an endless list of dreams.

``With both of them, there was so much room to project and imagine anything you wanted,'' said Simon, the author.

``You could project a future political candidate. You could project a great lover and romancer of women. You could project a down-to-earth guy. You could write a dozen biographies without even knowing the guy,'' Simon said.

``In a way, he's a receptacle for a lot of fantasies. That's what Diana was, too. And that may be the perfect definition of the ultimate celebrity.''

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2 photos

Photo: (1 -- color) Princess Diana

(2 -- color) JFK Jr.