Letitia Baldrige, who was social secretary to first lady Jacqueline Kennedy and also became known as a “doyenne of decorum” and chief arbiter of good manners in modern America, died Oct. 29 at the Sunrise at Fox Hill nursing facility in Bethesda. She was 86.

She had severe osteoarthritis with cardiac complications, said Mary M. Mitchell, a collaborator of hers.

In an 1978 profile, Time magazine described Ms. Baldrige as a “superbly energetic amalgam of feminist and Tasteful Lady.” Decades before women talked about “having it all,” and at a time when many of her female colleagues were afforded few professional opportunities, she embarked on a career that went from diplomacy to the White House to the top levels of business.

Discourtesy and arrogance were not requirements for a career of similar accomplishment, she would later advise executives in her role as a maven of etiquette.

“For every rude executive who makes it to the top,” she wrote in her “Complete Guide to Executive Manners” (1985), one of her numerous guides to politesse, “there are nine successful executives with good manners.”

The daughter of a Republican congressman from Nebraska, Ms. Baldrige began her career in the 1950s with the State Department.

But before she was given access to the world of high-level diplomacy, she was required to take a course that qualified her for secretarial work. This apparently had not been part of the curriculum at Vassar College, from which she graduated in 1946.

She was sent to Europe, where under the formal title of social secretary, she was an adviser to David K.E. Bruce, the U.S. ambassador to France, and Clare Boothe Luce, the U.S. ambassador to Italy.

Before joining the Kennedy White House, Ms. Baldrige was the public relations director — and reportedly the first female executive — at Tiffany & Co., the world-renowned New York jewelry firm. She later founded and ran Letitia Baldrige Enterprises, a public relations and marketing firm, in Chicago, New York and Washington.

And since the late 1970s, she wrote more than a dozen volumes of memoirs and books on etiquette, notably her updated version of “The Amy Vanderbilt Complete Book of Etiquette” (1978).

But she was perhaps best known for her years in the Kennedy White House, where she helped create and polish the enduring Camelot image of romance, elegance and sophistication.

The first lady, whose staff Ms. Baldrige joined in 1960, shortly after John F. Kennedy’s electoral victory, was a friend from their days at the private Miss Porter’s School in Connecticut. As Jacqueline Kennedy’s social secretary, Ms. Baldrige oversaw the glamorous social gatherings and state dinners for which the administration was known.

Ms. Baldrige was credited with helping arrange for a portable stage in the White House East Room where the Kennedys hosted jazz concerts, Shakespeare performances, ballets, musicals and opera. Ms. Baldrige issued many of the invitations to those events.

Sometimes her role called for apologies. The first official White House party, she wrote in her memoir “Of Diamonds & Diplomats” (1968), got her “into the hottest of water with our President.” Without alerting him, she broke precedent by arranging for hard liquor to be served at the Sunday evening event.

Despite an initial uproar over what President Kennedy called the “debauched” party, the White House continued serving hard liquor at official functions.

Ms. Baldrige traveled with the president and the first lady. In India, she recalled, she erred by preparing leather-framed photographs of the Kennedys as gifts for their hosts. Leather, made from cowhide, was unacceptable for Hindus.

For her, such mistakes became learning experiences and teachable moments. The president called her “Miss Push and Pull,” she once told The Washington Post, because “of my continuous attempts to make him conform to protocol when top-ranking officials from other countries were present.”

Ms. Baldrige left the White House in 1963. “I had had it,” she wrote of the exhausting hours and the demands of the job. She returned to the White House within several months to help the first lady plan her husband’s funeral and later wrote that her “years with Jackie remain forever front and center.”

Ms. Baldrige also worked as a consultant to first ladies Lady Bird Johnson, Patricia Nixon and Nancy Reagan.

After leaving Washington, Ms. Baldrige was hired by Merchandise Mart, a Chicago home-furnishings wholesaler that was in the Kennedy family. There she met Robert Hollensteiner, a real estate executive, whom she married in 1963. Shortly after their marriage, she opened her public relations firm.

In the 1970s, she began her career as a commentator on etiquette. Among her publications were a syndicated newspaper column and books including “Letitia Baldrige’s Complete Guide to a Great Social Life” (1987), with tips on meeting people, pulling off a great first kiss and social do’s and don’ts, and “Taste: Acquiring What Money Can’t Buy” (2007).

Letitia Catherine Baldrige was born Feb. 9, 1926, in Miami and grew up in Omaha. Her father, Howard Malcolm Baldrige, served in the House of Representatives from 1931 to 1933, giving Ms. Baldrige her first experience of social and professional life in Washington. Her brother Malcolm Baldrige served as commerce secretary during the Reagan administration until his death in 1987 in a rodeo accident.

Ms. Baldrige received a bachelor’s degree in psychology from Vassar and did graduate work in psychology at the University of Geneva before joining the State Department. From 1951 to 1953, she worked in Washington for the CIA in psychological warfare.

“In retrospect,” she told the New York Times, “what they were doing was not so different from public relations today.”

Besides her publications on etiquette, her books included “Roman Candle ” (1956), an account of her time in Italy; “Public Affairs, Private Relations” (1990), a novel about a public relations executive whose college friend is the first lady; and “In the Kennedy Style: Magical Evenings in the Kennedy White House” (1998).

Survivors include her husband, of Washington; their daughter Clare Smyth, who was named after Clare Boothe Luce, of Bronxville, N.Y.; their son, Malcolm Hollensteiner of Bethesda; and seven grandchildren.

In an interview, Mitchell recalled asking Ms. Baldrige once whether in all her high-flying work, she had ever suffered a lapse in self-confidence.

“Absolutely not,” Ms. Baldrige responded. She paused before adding, “But I’ve become a master of the apology.”