She is known as the most private Kennedy, ducking the press with her shy smile and downcast eyes, but today Caroline Bouvier Kennedy, 28 -- can she really be that old? -- will brave a pack of paparazzi to marry 41-year-old Edwin A. Schlossberg at 3 p.m. inside Our Lady of Victory Church down the road in Centerville.

Although observers here say there's not nearly the interest there was in cousin Maria Shriver's April nuptials to actor Arnold Schwarzenegger -- proving that Conan the Barbarian is definitely more gawkable than a man who writes poetry on plexiglass -- the needle on the Hoopla Meter is rising.

Shortly before 6 p.m. yesterday, the wedding party arrived in two buses at the church, which had been staked out by about a hundred well-wishers and reporters. Caroline, looking radiant in a silver and green dress cinched with a wide silver belt, slipped into the side door with her silver-haired, green-jacketed future husband. The rehearsal lasted one hour.

When the party exited, Sen. Edward M. Kennedy was barely able to fight through the crowd to his beat-up blue Pontiac convertible in the parking lot. He said today's wedding "will be a beautiful birthday present for my mother, who will be 96 years young" (Rose Kennedy's birthday is Wednesday). SK,2 SW,-2 ld,10 Appearing fit and very sunburned, Kennedy quipped, "This is number 10. We've got 20 more to go."

The rehearsal, according to the Rev. Donald MacMillan, a Jesuit priest and family friend who will perform today's ceremony, went "very smoothly." The wedding couple were "excited and happy but not nervous," he added. MacMillan said that the pair had chosen their own readings: "Caroline and Edwin seem to have a good grasp of scripture." Asked why the bride's mother, Jacqueline Kennedy Onassis, had not attended, the priest said, "She knows how to walk down the aisle."

After the rehearsal, the wedding party retired to the Hyannis Port Golf Club for a private dinner. The affair was described by one guest as a "warm, family-type occasion." The most moving moment of the evening, the guest said, came when John F. Kennedy Jr. stood and toasted his sister. "It's been the three of us alone for so long," he said, referring to himself, Caroline and their mother, "and now we've got a fourth."

Earlier in the day, the lovebirds were feted by friends and family with a luncheon cruise aboard a friend's sailboat, the Spray. At 3 p.m., the party disembarked at a small private pier adjacent to the Kennedy compound overlooking Lewis Bay in Hyannis Port. Onlookers were lucky enough to glimpse the bride-and-groom-to-be, as well as John Kennedy (still dripping in his bathing suit), Maria Shriver, Schwarzenegger ("I don't know what's going on either. I just got here") and novelist Susan Minot, a schoolmate of Caroline's, strolling up the lane to the compound. As photographers chased Shriver, she chased Schwarzenegger, who was stopped by a woman in a convertible. It turned out to be his mother-in-law, Eunice Shriver. "Are we playing tennis, Arnold?" she commanded. Schwarzenegger said they were, and he went off to change out of his baggy Hawaiian print shirt.

Minot stopped for a moment. She said that Shriver's wedding was much glitzier than this weekend's event. "Maria's in television," she said. "That was her scene. It's not their way," referring to the media-shy bride and groom.

A gaggle of celebrity-seekers stood outside the white fence, guarded by policemen. "That's Schlossberg in the yellow trunks," noted one woman authoritatively.

Workers have been sprucing up the compound grounds, and the huge white tent and dance floor are in place.

Ah, Camelot.

All week, the local newspapers have been salivating at the slightest crumb of marital trivia, from the groom's hobbies (art, skiing and gardening), to the 21 limos Cape Cod Limousine is providing, to what Caroline said to well-wishers who greeted her private Cessna jet when it arrived in Hyannis Wednesday afternoon from Martha's Vineyard. Caroline's message was short but to the point. "Hi," she said.

Shortly afterward, Kara Kennedy, daughter of Sen. Kennedy, arrived on a commuter flight. Both Caroline and Kara were reportedly coming from a luncheon held at the bride's mother's oceanfront home, and why Caroline didn't give her cousin a lift is anybody's guess.

The point is, nobody's talking. Observers say that's what the bride's mother has decreed. While Caroline sunbathed on the beach in an aqua blue bikini in front of the compound Thursday, one intrepid reporter followed Sydney Lawford McKelvey into the ladies' room at Hyannis Airport while she changed her 7-month-old son's diaper. "I'm very happy and excited," McKelvey, presumably struggling with a Pamper, was quoted as saying. "It's going to be fun."

Accompanying cousin Courtney Kennedy Ruhe was New York fashion designer Willi Smith, who designed the blue linen jackets and white pants for the ushers as well as the groom's untraditional linen suit.

Wedding chauffeur Maurice McElvoy was said to be upset with comedian George Burns, who was driven around town in the same gray and white stretch limo that will carry Caroline to the church. It seems Burns dropped a burning ash from his cigar on the red velour seat, leaving a small hole in the upholstery. The seat will be covered by a new white sheet.

There was also a lot of buzzing over whether President Reagan and First Lady Nancy Reagan would attend the wedding, but a White House spokesman said they were weekending at Camp David instead.

The guest list for today's ceremony and reception at the Kennedy compound is fairly small (425) and fairly typical, including a large number of friends of the mother of the bride and the usual assortment of Kennedy cousins and family, as well as a select group of Caroline's friends from the New York art scene.

Guests must present their watercolor invitations to security guards at the church and reception. Onassis has tried to keep the wedding as low-key as possible; there were reports that some family members were dismayed by the circuslike atmosphere at the Shriver-Schwarzenegger nuptials. The professional photographers she hired will not be allowed inside the church or at the reception to be held at the compound.

Maria Shriver got the nod as matron of honor, and the best man will be John F. Kennedy Jr., the 25-year-old brother of the bride. There will be seven bridesmaids, likely to include Susan Minot and cousins Courtney Kennedy Ruhe and Sydney Lawford McKelvey. They will wear pastel gowns. Venezuelan socialite-turned-designer Carolina Herrera designed the bride's gown, which is being kept secret. Like so much else.

The food will be by Glorious Foods, and will not be the boiled New England dinner erroneously reported, but the far more seasonal cold pea soup with mint roast chicken, cold sirloin of beef and raspberries. The wedding cake will be white, inside and out, sans the usual tacky plastic bride and groom on top. The ladies' coifs will be handled by Joseph Spadarl, hairdresser to the bride and her mother.

After the ceremony, the bride and groom are expected to give a brief press conference, then meet with Rose Kennedy, who is too frail to attend the wedding.

Caroline Kennedy, now a law student at Columbia University, was a few days shy of 6 years old when her father, President John F. Kennedy, was assassinated. She is indelibly branded in the American consciousness as a small girl with cropped blond hair, hiding under her father's desk in the Oval Office or perched atop a pony named Macaroni.

She grew up under the protective wing of her mother, her quiet, trustworthy behavior a direct contrast to that of her more boisterous cousins. According to Peter Collier and David Horowitz, authors of "The Kennedys: An American Drama," she and her brother John "had a regal poise all the others lacked."

Later, she is said to have obsessively collected coins and stamps commemorating her late father, and to have taken the name Joan as her confirmation name because Joan of Arc was a martyr.

Friends describe her as painfully shy, with a dread of celebrityhood. "But like her mother," gushed the Boston Herald this week, "who loves to dance and swap jokes with friends, Caroline has many moments of ebullience in private."

A few years ago, she took a job as copy aide with the New York Daily News. One day, she stopped at a nearby deli for lunch. The picture of her made it back to the newsroom, via the UPI wire, before she did.

After graduating from Concord Academy, where it is said she studied hard and sipped frappes at the local hangout with friends -- followed by Secret Service agents -- she enrolled at Radcliffe College. After graduating in June 1980, she moved back to Manhattan and took a job as a researcher in the office of film and television at the Metropolitan Museum of Art.

She dated a number of men, among them writer Tom Carney, but was unattached when she met Schlossberg, an artist, designer, poet, philosopher, gamesman, painter, scientist and inventor, at a dinner party in 1981. He reportedly gave her a VCR for her apartment, and the two became an item. Schlossberg, author of several books, has his own Manhattan company, which designs museum exhibits. He also has four degrees from Columbia University and a country home in the Berkshires. He is said to be a millionaire.

His 1968 book "WORDSWORDSWORDS" is really a box containing 17 poems written on various media, including aluminum, plexiglass and black cloth. Only 25 copies were printed.

Friends observe that he is extremely protective of his future bride. They also say he has been warmly accepted by the Kennedys, despite the difference in their religious backgrounds (Schlossberg is Jewish). "Everybody thinks he's great," Douglas Kennedy, son of the late Robert Kennedy, told reporters recently.

But the Kennedys are famously clannish, and breaking in is difficult for any outsider. "They probably won't ask him to play touch football on Thanksgiving afternoon," Barbara Gibson, former secretary to Rose Kennedy and author of "Life With Rose Kennedy," told one reporter recently. "But the family likes him."

In any case, according to a Schlossberg acquaintance, touch football isn't his style. "His idea of a game is to toss out quotes from famous philosophers and let people guess who said what."