It is difficult for an agency as old as J. Walter Thompson, which will mm 140 next year, to record some firsts at so venerable an age. But it will do just that with a rare changing of the guard. Thompson, which works for blue-chip advertisers like Diageo, Ford Motor, Kellogg, Merrill Lynch, Nestl6, Pfizer and Reckitt Benckiser, will announce today that Bob Jeffrey, president for its North American operations, will be promoted to chief executive, effective Jan. 1. Mr. Jeffrey, in being named the ninth chief executive of Thompson since 1864, succeeds Peter A. Schweitzer, who will become chairman, a post that is now vacant. Mr. Schweitzer, 64, will also relinquish his duties as worldwide president to Michael Madel, now president for the Thompson operations in Europe, the Middle East and Africa. Mr. Jeffrey, 50, will become the first Thompson chief executive to have spent most of his advertising career outside the agency. He joined Thompson five years ago as president of the flagship New York office he came from the agency now known as Lowe & Partners Worldwide, part of the Interpublic Group of Companies, where he had been executive vice president and managing director for the San Francisco office. Mr. Jeffrey, who was also a founder of the Goldsmith/Jeffrey agency in New York, was promoted to his current post in 2001. Mr. Madel, 53, will be the first Thompson worldwide president to be based outside New York, in this case London. Mr. Madel, who joined Thompson in 1990, adds responsibilities for the Asian-Pacific operations to the duties of his current post, to which he was promoted in 1997. The changes come as Thompson, the largest agency in the United States in revenue--and No. 4 globally, behind Dentsu, McCann-Erickson Worldwide Advertising and BBDO Worldwide---confronts some daunting challenges. While Thompson has recently gained additional assignments from clients like Pfizer, the agency has also lost some accounts from prominent marketers including the Miller Brewing Company division of SAB-Miller and Sun Microsystems. Thompson has had to shake up the ranks of senior managers at offices in cities like Chicago, Detroit and San Francisco to help reassure clients. The agency stumbled in efforts to develop an entertainment marketing division, dismantling a unit based in New York named Content @JWT in favor of handling those tasks out of the Detroit office. And Thompson, like many large agencies, is deemed in need of improving its creative output, particularly as clients must deal with rapidly changing marketing and media trend. The challenges include the rise of the finicky youthful consumer cohort known as Generation Y and the need to develop alternatives to traditional ad forms as consumers zip, zap and fast-forward television commercials. One task facing Mr. Jeffrey is to take the J. Walter Thompson creative product to an even higher level. Another is to ensure that communications solutions for clients are coordinated across all disciplines as effective as possible. This referred to the Thompson offerings in areas as disparate as advertising, entertainment marketing, interactive marketing, direct marketing and health care advertising. Mr. Jeffrey, in a separate interview, acknowledged the scale and scope of what he would face. 'If you watch the movie Catch Me if You Can set in the 1960's, you see the prominent brands are Pan Am and T.W.A.,' Mr. Jeffrey said. 'Forty years later, look at the airline industry. If you look at the ad industry, you could prognosticate something similar,' he added. 'If we don't get our acts together, that could be us.' It can be inferred from the passage that the advertisers that I. Walter Thompson works for are ______.