For four generations the 28-room hilltop mansion has presided grandly over Newport, R.I. and Narragansett Bay—a period monument to statelier times where the ghosts of men in sailing whites and women twirling parasols still seem to play on the vast sloping lawn by the sea. As the summer residence of the Auchincloss family, the estate called Hammersmith Farm was the setting for Jacqueline Bouvier's debut—and for a gala reception after her marriage to the dashing young senator from Massachusetts, John F. Kennedy.

But Hammersmith, like many of Newport's other great homes, seems finally to have succumbed to modern times. This summer, less than a year after her husband Hugh's death, Janet Auchincloss, Jackie's mother, has reluctantly put the family manor up for sale. "Hugh and I wanted to keep the farm for our descendants," she says, "but it was absolutely necessary to sell."

The reason, she frankly concedes, is financial: high taxes ($31,224), horrendous maintenance costs and a precipitous drop in the Auchincloss fortune. "My husband did a very noble thing and used his money to save his brokerage firm in Washington," she says, "so we've known for seven years we had to sell it." In addition to the main house with its 10 master bedrooms, the 54-acre barony includes a 16-horse stable, a playhouse and even a small cemetery for the family's pets. The asking price is $985,000. Not for sale are a two-bedroom house (c. 1720) called the Castle, where Mrs. Auchincloss lives with two Jack Russell terriers, and the Windmill, a house at the water's edge. "All the children want to stay there when they visit," she says happily. "I have 13 grandchildren, you know." ("As I get older," she adds, "I get more and more interested in genes.")

Perhaps the most exciting times at Hammersmith were the years of her son-in-law's Presidency. JFK's arrival would be signaled by "the garbled phone equipment they came and put in," she remembers. "Jack would land by helicopter, and the Honey Fitz would be at the dock." (It is the same dock used by Robert Redford in The Great Gatsby.) Still, Mrs. Auchincloss brushes off the suggestion that Hammersmith be turned into a Kennedy memorial. "Nobody loved Jack more than Hugh D. and I did," she says, "but he only came here one month of the summer, and sometimes he'd tear back and forth to Washington."

When she married Hugh D. Auchincloss 35 years ago, Janet Bouvier balked at living in Newport. "I had grown up in East Hampton, Long Island," she explains, "and that ocean is still my ocean. But we lived here and it was very good for the children." Among the children who had the run of Hammersmith: Jackie and Lee (Radziwill) by Janet's first marriage, three more from his and, later, two of their own, Janet and Jamie. Jamie hosted one weekend party for 44 girls (who slept in the house) and 44 boys (who were quartered above the four-car garage). "It was just like boarding school," Mrs. Auchincloss recalls wistfully, "but I spent the next few weeks sending back the tennis rackets and sneakers they had left behind."

After World War II Hammersmith began to change, she remembers. Of 32 men who had once tended the grounds, only the superintendent and two old family retainers were left. "There was a time when the second man would serve tea in the garden—and then there wasn't even a first man." In the late 1940s the family asked the Olmsted firm, which had designed the formal grounds, to come back and simplify them. "The sunken gardens were removed," she recalls, but the formal rose garden remained. "I tried to keep it up," she says. "I was always asking Jackie and Lee and everybody to come down and weed it." The rose garden is gone now too.

Mrs. Auchincloss will continue to summer in Newport, spending the winter at her townhouse in Washington, and she trusts that Hammersmith will not go to a developer. "It's been a farm since 1640, the only farm left in Newport," she says. "It would be a tragedy if boats had to pass a bunch of condominiums." Her superintendent of 10 years, Manny Faria, 53, is also uncertain about the future. "When you work for them, you're part of the family," he says, adding confidentially: "It's not one of those places where you have to walk in through the back." It was Faria himself who reminded Mrs. Auchincloss of the stoic motto on the Hammersmith crest which translates, "What Shall We Do Now?" Janet Auchincloss, at 68, seems gracefully resigned to the answer. "After all, I'm able to keep part of what we love," she says, "and we do have all the memories."