Caroline Bouvier Kennedy, 28, will marry design executive, poet and author Edwin Arthur Schlossberg, 41, this summer, and already his acceptance into the tight-knit clan seems assured.

The two have known each other "for quite a while," Douglas Kennedy, Caroline's cousin and a son of the late Robert F. Kennedy, said yesterday. "Four or five years . . . Everyone thinks he's really great. He's very intelligent and everyone is very fond of him. They come to the family a lot. We see them a lot in Hyannis Port."

Schlossberg accompanied Caroline to the memorial service at Washington's Trinity Church on the 20th anniversary of her father's assassination.

The couple has been together for "about three years," Edwin's father Alfred Schlossberg said yesterday from his home in Palm Beach. "I've gotten to know Caroline. She's a lovely girl." He would not comment further on their relationship. "I think that's private."

Yesterday, there were few details available on the wedding plans, but that may have been because they weren't yet made.

"Mrs. Onassis is handling all that," Alfred Schlossberg said. "I think they're discussing that this weekend . . . the day or the place, whatever."

Schlossberg, who has a doctorate in science and literature from Columbia, is president of Edwin Schlossberg Inc., a museum interior design firm.

He has also written nine books (including "The Philosopher's Game: Match Your Wits Against the One Hundred Greatest Thinkers of all Time" and "Pocket Calculator Game Book") and has exhibited lithographs of his poetry, at least one done in thermal ink that changes color with temperature, in New York.

Also among his works are a participatory farm exhibit for the Massachusetts Society for the Prevention of Cruelty to Animals and a recorded "sound work," described by The New York Times in a 1982 review as "an exceedingly boring meditation," featured on an album called "Revolutions Per Minute."

Alfred Schlossberg, whose family is Jewish, said he did not know what form of ceremony the wedding would take. The Kennedy family is Catholic.

"I'm not too sure about" the religious question, said Douglas Kennedy. "I'm sure there's going to be some sort of Catholic service in the wedding. I don't know if it's going to be a full Catholic service."

Caroline, the elder child of President John F. Kennedy, was 6 years old when her father was slain and, together with her mother and brother, has spent her life trying to avoid the media spotlight.

Her relationship with novelist Tom Carney in the late 1970s was widely expected to result in marriage, but Carney married photographer Maureen Lambray in 1980. Kennedy went to Concord Academy high school in Massachusetts, graduated with a bachelor of fine arts degree from Harvard University's Radcliffe College, and has had an active interest in film and photography.

Her photographic interests have resulted in a stint as a copy aide with the New York Daily News, a photo assignment covering Elvis Presley's funeral for Rolling Stone magazine, and a former job as manager and coordinating producer in the Metropolitan Museum of Art's office of film and television. She is currently a first-year law student at Columbia University.

The wedding story might not have the oomph or the ooh la la one might expect in Palm Beach, where both families have homes. It was news to Agnes Ash, publisher of the Palm Beach Daily News (a newspaper known widely as The Shiny Sheet) and, at the same time, not news. She hadn't heard of Alfred Schlossberg, retired president of the New York textile firm of Alfred Schlossberg Inc., she said, "and you know, I make it around to all the parties . . . "

The announcement "doesn't sound as spectacular as her cousin's boyfriend, Arnold Schwarzenegger," she said, referring to Maria Shriver's engagement to the musclebound movie star. "Now there's something -- everyone knows about Schwarzenegger . . . "

"Of course everyone wants to know who Caroline is going to marry. And they're just as interested in who John [Caroline's brother John F. Kennedy Jr.] is going to marry."

Told of Schlossberg's age, she said, "That's not so much. But I didn't realize she's 28 already. I imagine they'll talk about the difference in age, too."