The tables in the ornate turquoise-and-pink Park Avenue dining room were festooned with enormous bouquets, and the elaborate place settings included four glasses, three for wine. Seated around the hostess — ten per table — were some of the most powerful men in the country and their wives: president-elect Ronald Reagan and Nancy; Walter Wriston of Citibank; William S. Paley of CBS; Felix Rohatyn, the Lazard Freres financier reputed to have saved the city from default in the late 1970s, and a host of others.

A smallish, older woman in a short black lace dress stood up and proposed a toast. “America is in a sad state, but we can put our shoulders to the wheel,” Brooke Astor told her guests, who had gathered to fete the president-elect. “Big oaks from little acorns grow.”

Having being toasted in return by Reagan, she returned to her chair at the focal point of the room, between the president-elect and Henry Kissinger, whose wife, Nancy, wore a Bill Blass python jacket. (The jacket’s designer was a guest, too.)

Suddenly, Mrs. Astor noticed she was missing a diamond earring. And that is how it happened that the president-elect of the United States of America ended up crawling on his hands and knees beneath Mrs. Astor’s dinner table.

Her apartment was among the most tasteful and luxurious in New York, occupying two floors, plus an additional apartment for guests. The décor was by fashionable decorators like Mark Hampton and Parish-Hadley, who created for her a famous sang-de-boeuf library that epitomized her dedication to œuvres littéraires.

Likewise, Brooke Astor was a byword for stylish dress.Traveling to inspect the projects she’d funded around New York, whether at the Metropolitan Museum of Art or at a settlement house in Harlem, she was inevitably “the little lady with the big hat,” unmistakable and perfect. “People expect to see Mrs. Astor, not some dowdy old lady,” she once said. “And I don’t intend to disappoint them.”

Flash forward a quarter-century from the Reagan fete, and New York has reinvented itself. The Vincent Astor Foundation spent itself into oblivion nearly a decade ago, but Mrs. Astor, now 104, is quietly living out her dotage on Park Avenue. But, oh, what a fall from grace.

Her slide from top society hostess to lonely old lady is complete. The designer dress on which her diamond earring was finally discovered, snagged on the lace, by Reagan has been replaced by a tattered nightgown. Her Esteé Lauder cosmetics have been exchanged for Vaseline. Her heirloom chintz has made way for a chilly couch that smells of urine.

Ugly scenes are bruited about: an ungrateful son pushing his senile mother aside, forcing her to sign over to his wife her beloved Maine vacation home. How far it all is from the glory that once was Mrs. Astor, the gold standard of both society and philanthropy.

She had a gold-plated name — for it was her husband’s grandmother Mrs. William Backhouse Astor who had originated the concept of “the Four Hundred,” the cream of New York society and the maximum number of guests who could fit in the ballroom of her Fifth Avenue mansion.

But if her name could open doors, and her fortune would make even a banker whistle, Mrs. Astor’s success as a philanthropist was not due to these factors alone. Any billionaire with a conscience can tell you it is hard to give away a fortune; harder than making one, some say.

Her combination of glamour, wealth, savvy, conscience, and patrician grace created in her a kind of perfect storm of philanthropy, one that helped create a renaissance in New York, especially in its elite institutions. And she had a ball doing it.

From her earliest days as a child in China, where her father was a Marine Corps commandant in Peking, to her middle years as an editor at House & Garden magazine, right through 1998, when she shut down her philanthropy after distributing about $200 million to projects she personally oversaw, Mrs. Astor was always absorbed with the passing parade.

Her memoir “Patchwork Child” includes photos of decapitated criminals she saw in the streets of Peking, and acutely observed pen portraits of avant-garde young women she encountered in Greenwich Village. Her writing style was cool, yet engaged. She watches herself with great curiosity in “Patchwork Child,” and again in “Footprints,” which takes the story through her marriages.

Even when her philandering husband breaks her jaw when she is six months pregnant, Brooke Astor the author never descends into a writerly fury. She stands by her awful first spouse until he finally kicks her out. Even then she waits until he is safely elected to state Senate in New Jersey rather than subject him to the bad publicity of a divorce during the campaign.

He makes a brief return after a few decades to put the touch on her for a few bucks. He has five wives and dies penniless; Mrs. Astor calls him “wretched.” Years later, she told an interviewer, her big mistake had been getting married so young: “At the age of 16, you’re not jelled yet.”

Her first husband left her for a floozy and her third husband left her the Astor fortune, but the real love of her life, one learns with pleasure, was her second husband, Charles Marshall, a well-to-do broker she married in 1932. The Marshalls honeymooned aboard the Europa, bound for Cherbourg, and spent each summer in a castle in Portofino, Italy. Lillian Gish called it “one of the greatest love stories” she had “ever been near.”

Marshall died in her arms on Thanksgiving Day, 1952.

Had she not married for a third time, Brooke Marshall might have become a society tea matron — she had met the eligible Marshall while riding to hounds — and a fine if undistinguished magazine editor with a comfortable lifestyle. But much as Mrs. Astor loved taking tea, she loathed society teas.

Next came Vincent Astor, not a monster, but a piece of work all the same, who laid siege to her only months after Marshall’s death and succeeded in marrying her. He was a depressive, perhaps an alcoholic, and enough of a control freak to forbid her to be on the phone when he was at home. Yet he was also civic minded, sat on the boards of the library and the zoo, and seemed genuinely to have adored her.

As he lay dying in 1959, Vincent Astor told his wife about the foundation he was leaving in her charge. “You are going to have a hell of a lot of fun running it, Pookie,” he said.

The Vincent Astor Foundation was established in 1948 for the noble if unspecific purpose of the “amelioration of human misery.” It was Mrs. Astor’s great inspiration that, since the bulk of the money had come from rents paid on Astor land in New York — they supported “Astor Flats” that included some of the worst slums in the city — the Astor largesse should be bestowed upon the ground on which it was made.

Mrs. Astor announced to her dead husband’s astonished retainers that it would be she who made the decisions. She sold Newsweek magazine, which Vincent had helped found. She settled a bitter challenge to the will from Astor’s half-brother. Then, she was off to the races.

Among the first grants was $1 million made to United Neighborhood Houses, in support of a program to keep teenagers at settlement houses from joining gangs. Coming in 1961, the same year the film “West Side Story” won the best picture Oscar, it was a surprisingly prescient grant and one that helped set the tone for a foundation that would not confine its giving to the favored charities of the Four Hundred.

But the institutions Mrs. Astor liked to call the city’s “crown jewels” were hardly neglected. John Jacob Astor, the butcher who came to New York in 1783 and died in 1848 after becoming America’s first millionaire, was one of the founders of the New York Public Library, and his descendants continued to support it. Mrs. Astor sat on the board of the library after her husband’s death and became its leading light.

In 1963, the foundation gave a half-million dollars to convert the Arnold Constable department store on Fifth Avenue and 40th Street into the Mid-Manhattan Library. It was the beginning of a beautiful relationship that included $5 million in 1977 to improve collections, and $10 million in 1985 for research libraries.

In 1983, Mrs. Astor announced she was giving up all her other board memberships to concentrate on the library, a move the library credits with focusing attention on its needs to the extent that, in the words of its current president, Paul LeClerc, “It recalibrated the aspirational level for libraries all over America.” She remains honorary chairman of the board of trustees.

Other crown jewels on the Astor tiara include Carnegie Hall, Columbia University, the Morgan Library, the American Museum of Natural History, and the Bronx Zoo, where the foundation funded “The World of Darkness” exhibit, featuring bats and naked mole rats.

The zoo honored her by naming its first baby elephant “Astor” in 1981. It is unclear whether the gesture included a reference to her lifelong affiliation with the Republican Party.

There are any number of things named for Brooke Astor around the city. At the Metropolitan Museum, there is the Astor Court, a Chinese garden reflecting her love of the country where she spent several years as a child. The Bronx Zoo has an Astor Court, too, near the “World of Darkness” exhibit.

And so even as life slips away from Brooke Astor — the last of the Astors, in fact — her name and works will live on in New York City. The city itself is her own best memorial. She seemed to show some awareness of this even back in 1984, when she told an interviewer, “I re-created myself. Now I feel I’ve become a public monument.”