Letitia Baldrige, 86, the imposing author, etiquette adviser and business executive who became a household name as Jacqueline Kennedy's White House chief of staff, died on Monday in Bethesda, Md.

At 35, Baldrige, left her job as public relations director for Tiffany & Co. to help out a fellow Vassar alum, the former Jacqueline Bouvier, becoming, in essence, the social secretary of the Kennedy White House as it emerged as a center of culture, art and youthful elegance.

Baldrige left the White House in June 1963, less than six months before President John F. Kennedy's assassination, to work for the Merchandise Mart, a Kennedy family business enterprise in Chicago. She went on to found her own public relations and marketing business.

In the 1970s, she established herself as an authority on contemporary etiquette, writing a syndicated newspaper column on the subject and updating "Amy Vanderbilt's Complete Book of Etiquette" in 1978. Baldrige's face soon appeared on the cover of Time magazine, which hailed her as the nation's social arbiter.

After that, her own name was enough to attract readers, and in 1985 she published "Letitia Baldrige's Complete Guide to Executive Manners," which dealt with behavior in the workplace and outside it.

Baldrige, who stood 6 feet 1 inch tall and became known for her elegant silver hair, long contended that the heart of all etiquette was consideration for other people, rather than a rigid set of rules. "There are major CEOs who do not know how to hold a knife and fork properly, but I don't worry about that as much as the lack of kindness," she said in 1992.