NANCY REAGAN has a walker. It is not a three-sided steel device to help her make her way through the White House corridors. The next first lady's walker is a squat, chubby, foppish, 66-year-old Manhattan multimillionaire real estate heir with a Humpty Dumpty head who reeks of sandalwood perfume, loves to nibble sweets, carts as many as 86 pairs of cufflinks with him for a weekend out of town and has reigned for decades as the flamboyant prince of New York society gossip.

His nickname is Baby Zip and his real name is Jerry Zipkin, but he has been known as The Walker ever since Women's Wear Daily coined the phrase in an article about those perennial bachelors whose raison d'etre is to entertain and escort rich ladies with busy husbands. Zipkin had a sizable bevy of matronly beauties for whom he performs the same function, but it isMrs. Reagan who may just make him a household word. Zipkin's friendshiip with the future first family may prove to be the most entertaining aspect of the new administration. It is precisely this thought, say some insiders, that is putting little beads of anxious sweat on the earnest brows of Reagan aides.

Nancy Reagan's fondness for her colorful friend is as out of keeping with her standard suburban image as an unraveled hem would be on one of those Adolfo knits. Maxine Cheshire, quoting an acquaintance of Mrs. Reagan's, says that the favorite pastime of the president-elect's wife is lunching with Zipkin at Le Bistro in Los Angeles, "listening to him gossip about everyone they know." Mrs. Reagan has pronounced her pal "a sort of modern-day Oscar Wilde. He has more depth than a lot of people in our lives," she told one interviewer. "He is constructive, has an ability to amuse everyone, from our driver . . . to the sternest Secret Service agent."

Zipkin has been walking Nancy for about 15 years now, ever since -- as his and Nancy's chum Betsy Bloomingdale puts it -- he "gravitated" toward the Reagans and their California coterie of rich friends -- the Bloomingdales, Jane and Justin Dart, Bonita and Jack Wrather, Earle and Marion Jorgensen. He squires her to Monsieur Marc, her New York hairdresser; he takes her shopping for couturier clothes on Seventh Avenue. He takes her to museums and to the ballet and to the theater and to cozy, chatty lunches and suppers. He kept her company during the tense hours of the Kansas City convention in '76 and again this year in Detroit (in Kansas City, he even shared a box with the Reagans and subbed for Nancy when she couldn't attend one fete) and entertained her whenever the campaign brought her to Manhattan.

Mrs. Reagan, says Mrs. Bloomingdale, relies on him for his "marvelous ideas and suggestions about clothes -- whatever. We think he's terrific. When he says something to Nancy or Nan or me -- you know, your skirt's too long, something like that -- you say, 'Stop! Stop!' Then you think about it, and say, 'Well, maybe he's right.' Jerry's got that eye for the perfect detail. He always tells the truth; he doesn't care. He's never phoney-baloney.

Though Zipkin is still more closely allied with Mrs. Reagan than with her husband, both feel warmly enough toward Zipkin to have included him in some of their most special campaign moments. On nomination night in Detroit, Zipkin, the Bloomingdales and a few other friends celebrated with the Reagans in their hotel suite and attended several late parties with them. Zipkin and the Bloomingdales also rode in the post-election motorcade to the Century Plaza hotel in Los Angeles after they and the Reagans ate dinner at the Jorgensens'. And the couple "took him seriously," says Betsy Bloomingdale, when he counseled them to allow Patti and Ron Jr. to talk to Interview magazine. "Jerry's word would have made a difference," says Bloomingdale. "He's rarely wrong."

A lot of people treat Jerry Zipkin with all the respect due a mediocre court jester. To them, he is simply one of the sillier fixtures of New York society, whom the whim of history has plopped down behind the presidential petticoats. Jokes are buzzing around New York and Washington about Zipkin's appointment to a post in the "kitchen cabinet" -- though few seriously anticipate he will be given a bona fide post of any kind, least of all Zipkin. ("Oi vey," he replied when a friend suggested he take on the Israeli ambassadorship.) Women's Wear's only acknowledgement of his new status as presidential intimate has been to change its other sobriquet for Zipkin -- the Social Moth -- to the Social Mouth.

One longtime observer calls Zipkin a "nebulous, bitchy, very, very, pretentious and affected" man interested only in "sophisticated girl-talk." Another dismisses him as "an awful sucker-up to the rich." Even his buddies are obliged to admit that one really must know Jerry to love him; his manner, in the words of one frank friend, tends toward the "snide, haughty, comtemptuous and sneering." Truman Capote once tried to sell a chapter of "Answered Prayers" to Esquire by verbally describing to its editor a lengthy scene in which the heroine enjoys a gossipy tete-a-tete on the telephone with a character based on Zipkin. Perhaps because the two are not unalike in looks and personality, Capote has never much cared for Zipkin. Capote's favorite put-down for Zipkin is that his face is shaped like a bidet.

Zipkin's army of devoted friends do not poke fun at him. The best and closest ones are women, of course: Betsy Bloomingdale and Nan Kempner and Pat Buckley and Chessy Ranier and Mica Ertegun. And Diana Vreeland and Diane von Furstenburg and Mary Lazar and Estee Lauder and Mary McFadden and Jan Cowles and Lady "Slim" Keither and Louise Melhado. But he has a bunch of male friends as well, among them Bill Blass and Mortimer's restaurant owner Glenn Birnbaum, (both of whom he has known for more than 30 years), Alfred Bloomingdale and Ahmet Ertegun. And, when Nan and Pat and Mica and Chessy threw him a birthday party four years ago at Elaine's, Pat's and Mica's and Mary's husbands all stood up to give flattering speeches about him. "They're all different," Zipkin has said of his friends. "It's not a question of being chic. All my friends are chic."

His fans trill his praises, and their compliments make him sound not unlike a party balloon: He is, they say, bright, light, gay, amusing, festive. Diana Vreeland says she has adored him for 20 years: "He's a naturally affectionate person, and his friends rely on him."

Of course his friends are devoted to him. He dotes on them. He ladles out advice about must-see cultural events, news about who's visiting the city, parties to go to, and the tastiest gossip in town. Zipkin is to New York gossip what air traffic control is to arrivals and departures at Kennedy airport. "Everybody clears with Jerry when they come into town," says Birnbaum. "They're immediately on the phone with him. He's a fountainhead of information."

He is also a prodigious gift-giver, forever sending books and objets d'art to friends, sets of china to newlyweds. Years ago, when Liz Smith found herself out of work, he called to tell her that if she needed money she had better ask him or he'd kill her. "He's got a very big heart," says Smith, "that he covers with a chi-chi veneer. Underneath it all he's a sentimental slob."

Monsieur Marc says that many of his customers were referred by Zipkin. "I would like to do something for him," says Monsier Marc. "I can't, though. He's bald."

But it is Jerry Zipkin's rabid loyalty to his friends that earns him the most resounding praise -- as if , in a subculture where betrayal lurks behind the next banquette, mere faithfulness deserves the highest accolades. "When he's your friend," Mrs. Reagan has said, "he's really your friend. He has a deep sense of loyalty." Nan Kempner agrees: "He keeps confidences like no one you've ever seen. He's leakproof." It was Zipkin who leaped, as it were, to high society's rescue as the official spokesman for their outrage in 1975, after Esquire published "La Cote Basque 1965," the chapter from "Answered Prayers" that detailed the naughty goings-on of characters with unmistakable resemblances to many of Zipkin's friends -- including the Duchess of Windsor, Slim Keith, Nedda Logan and the Paleys. "Disgusting!" he yelped to Liz Smith. "It's disgusting! Truman is ruined. He will no longer be received socially anywhere." Though some deny it, others recall a skirmish between Capote and Zipkin after the story was published, in which the two men bumped into each other outside Le Bistro, had an angry spat, and may have given each other a provoking nudge or two. "I'm very hip," Zipkin once told Women's Wear, "on the subject of loyalty . . . I have a very strong feeling about my friends. They can do no wrong, they're absolutely perfect."

Zipkin, however, is not called the Social Mouth for nothing. "He's not a goody-goody; he takes stands," admits one friend. "It can be pretty awful when you don't stay on his good side."

"Jerry's got a very sharp tongue," Bloomingdale confesses. "We were at a barbecue once in California, and he looked down at one of the men's shoes and said, 'ugh!' Who wears Gucci buckles anymore?" The man went into a swoon!" Another time, she says, he walked into a friend's house and spotted an artificial flower arrangement. "Ugh!" he said again. "What are you doing with artificial flowers?" The woman was devastated, Bloomingdale reports, but the next time she called on her there wasn't a fake flower in sight.

The Princeton yearbook for the class of 1936 has a photo of graduating senior Jerome Robert Zipkin, pudgy even at 22, and an entry stating that he is the son of Annette Goldstein and David Zipkin, a "real estate operator," has one sister, and lives at 1175 Park Ave. Young Zipkin, it continues, prepared at the Hun School, a middling boys' school in Princeton. At Princeton, he did not accrue any academic honors, join any of the prestigious campus eating clubs, or act as officer of any of his extracurricular clubs or teams. The entry closes with Zipkin's intention to attend Harvard Business School "and to engage in banking."

Zipkin never did either -- in fact, he never managed to graduate. Presumably he took up residence in Manhattan in his parents' apartment (he has called himself a New Yorker "born, bred and buttered") and commenced traveling and socializing. He flew to California often, where his intimates included George Cukor, decorator Bill Haines, Louis B. Mayer and his wife, Claudette Colbert, and Paulette Goddard. At some point, probably in Europe, probably in the mid-'40s, he met Somerset Maugham. According to Ted Morgan's recent biography of Maugham, Zipkin became one of Maugham's favorite bridge partners and a "warm and enduring friendship" grew between the "ebullient real estate heir" and the writer.

In 1949 Zipkin took his first trip to the Riviera, to stay with Maugham in his home. After he left, Maugham wrote private secretary Alan Searle to say that Zipkin had gone on a "completely mad" spending spree during his visit. "We had the greatest difficulty in preventing him from buying up the entire contents of every shop he went into," wrote the author. "As it was, he went back laden with antiques, shirts and pullovers, most of which he could have got in New York at half the price. But as he owns not apartment houses on Park Avenue but rows of apartments, I don't suppose it mattered."

He visited and corresponded with Maugham and Searle until the last days of Maugham's life. Morgan suggests that Elliot Templeton, the snobbish character in "The Razor's Edge" who devotes his life to knowing the right people, may well have been based in part on Zipkin.

Zipkin returned the writer's friendship with a characteristic show of sentiment. In the mid-'50s he paid 2,600 pounds at auction for a "Moon and Sixpence" manuscript -- a world-record price for a manuscript by a living author -- and went on to amass a colossal Maugham collection. By 1966, when he sold it to the University of Texas, it consisted of more than 500 pieces.

Over the years, in between the trips to Palm Beach, to the Riviera, to California, to Spain, Zipkin has lived in the same Park Avenue apartment. The expansive bachelor pad reflects what Nan Kempner calls his "very catholic tastes" and overflows with his beloved possessions: an eclectic assortment of books, paintings, prints, photographs, sculpture, (including works by Clyfford Still and Henry Moore, a particular favorite), as well as more classical pieces) and his collection of fine boxes. Women's Wear, allowed in for a rare interview several years ago, noted that the apartment was perfumed with the "cypress scent of a Riguad candle" and pronounced the place "chi-chi"; one friend calls it "very Jerry."

Zipkin has done little entertaining in New York since his mother, who shared the apartment with him, died several years ago. He now holds court chiefly in restaurants: La Grenouille, Pearl's, Mortimer's, the Palm, Quo-Vadis. He sleeps there, he reads there and perhaps most important, he gets dressed to go out there. Zipkin is finicky about his hand-made shirts and suits The suit buttons are purchased in London). Once, the story goes, he informed the management of the Colony Hotel in Palm Beach that the closets in his room were too small and were hurting the shoulders of his suits. cThe owner obliged him by ripping out the closets in the room and installing new ones overnight. Unimpressed, Zipkin checked out the next day, never to return.

(Another of Zipkin's sartorial eccentricities is a pair of velvet evening slippers embroidered with a hammer and sickle which the strict conservative loves to wear out of an evening.)

Zipkin either has no love life, it seems, or is impressively discreet about it; friends profess to know nothing on the subject. "He's very private," says Nan Kempner. "As much of a confidant as he is, he didn't tell anyone when he had a pacemaker put in. He has a side that's less obvious than his jolliness." Another friend theorizes that he is probably inactive romantically: "He'd just rather go to fashion shows with ladies." The infrequent nights he does not go out he often spends poring over art magazines."

"He's a fascinating person," says a longtime friend, "and being a close friend of Mrs. Reagan's is going to make him even more fascinating."