THE MEDIA BUSINESS; A Shaper of Magazines Retires

Marshall Loeb, one of the most visible and influential editors in the magazine industry during his 38-year tenure at Time Inc., is to retire as managing editor of Fortune magazine after eight years in the job, the magazine will announce today.

Mr. Loeb will turn 65, the mandatory retirement age for Time Inc.'s managing editors, at the end of the month. He will become Fortune's editor at large and write a new column for the magazine.

He will be succeeded on May 20 by Walter Kiechel 3d, an executive editor at Fortune who joined the magazine in 1977 as a reporter-researcher. Mr. Kiechel, who is 47, will be the first managing editor in 40 years to be promoted from within the ranks of the magazine. Similar Visions

Mr. Loeb and Mr. Kiechel have worked together for several years and, by both their accounts, have similar visions for the magazine.

During Mr. Loeb's tenure, the "big story" that had always been Fortune's forte was made more explicit. In addition to standard fare about the economy, management and corporate strategy, Mr. Loeb introduced articles on executive life and on social problems that affect the business world. Homelessness and the plight of public schools were among the recurring themes.

He also expanded the use of graphs, lists and tables to illustrate major articles.

The change at Fortune comes as competition from television, newspapers and other business magazines is stronger than ever.

For instance, Biz, a monthly that focuses on small businesses, was started in March with an initial circulation of 500,000, as a joint venture between American City Business Journals Inc. and Dow Jones & Company. And the two monthlies that entered the field in 1992 have grown rapidly: Worth, which was started by Fidelity Investments, now has a circulation of more than 300,000, and Smart Money, started by Dow Jones and the Hearst Corporation, has a circulation of 449,000.

But the three magazines that continue to dominate are Business Week, Fortune and Forbes, despite their distinctly different thrusts. Business Week emphasizes news. Forbes, published every two weeks, focuses on how companies are managed and the people who manage them. And Fortune, also published every two weeks, is known for its in-depth articles.

The competition among the three for circulation and advertising is perhaps the fiercest in the magazine industry. "The last 10 years have been sort of nasty in the ways that Forbes and Fortune have gone at each other, with each trashing the other whenever they can," said Steve Klein, media director and partner at Kirshenbaum & Bond, an ad agency.

In North America, Business Week is the circulation leader at 883,718, followed by Fortune at 786,619 and Forbes at 770,008, according to the most recent figures from the Audit Bureau of Circulations. Fortune and Business Week also have international circulations -- Fortune at 136,753 and Business Week at 116,857.

Last year, Fortune saw a 10 percent increase in advertising pages, while Forbes had a gain of 1 percent and Business Week a decline of 2 percent. Through this March, Fortune's ad pages were up 8 percent, compared with the first quarter of 1993. Business Week was up 16 percent and Forbes was down 9 percent.

While Fortune officials decline to provide figures, they say the magazine's revenues are strong and profits are up. In 1993, circulation profits reached a record high, officials said.

Fortune has also prospered editorially under Mr. Loeb, who was previously managing editor of Money, a Time Inc. publication that emphasizes personal finance.

"I think Marshall really has a sense of the pulse of a magazine's readers, almost like no one I know," said Norman Pearlstine, a former executive editor of The Wall Street Journal and the president of Friday Holdings, a media investment group. "If you think of Money and Fortune, you see that he clearly positioned each of those publications just wonderfully."

A hurdle for Fortune was its image as the publication for the white-collar work force of Fortune 500 companies. With that audience shrinking, the trick was not only to keep the audience but also to build it.

Steven Swarz, editor of Smart Money, sees Fortune as a strong service publication for executives. "I think Fortune became must reading for people aspiring to higher corporate jobs and for people who wanted to know what those jobs were like," he said. No Big Changes

Mr. Kiechel said that while he was not contemplating a redesign or other big changes at the magazine, he would probably "rethink" some departments. He talked about adding more case studies and extracting lessons from them.

Long regarded as the heir apparent, Mr. Kiechel has overseen much of the magazine's coverage of managerial issues and, for 10 years, has written a column called Office Hours. He has also written many cover articles, including last year's "How We Will Work in the Year 2000."

He says the 1990's will be a defining time in economic history, comparable in importance to the industrial revolution in the 19th century.

"We are in a historic transformation of our economy," he said in an interview. "The core infrastructure is shifting from old industries like the auto industry to computers, telecommunications and the entertainment business. The old blue collar-white collar distinctions are going. The new workers are professional and technical workers who are going to be the dominant people in the work force."

The changes, of course, present new challenges to a business magazine. Mr. Kiechel even held out the possibility that the magazine might have to redefine its landmark Fortune 500 industrial list. Continuing Themes

Mr. Loeb said he would write about "forward-looking ideas" in his new column. He is also working on a book on personal finance and will continue to travel and give speeches around the world.

With his cheerful personality and relentless curiosity, Mr. Loeb has long had the air of a little boy who can't believe he is so lucky as to live the life he does. Brought up on Chicago's West Side, he served as a foreign correspondent in postwar Germany, became a reporter for The St. Louis Globe-Democrat and joined Time magazine in 1956, where he wrote or edited more than 130 cover articles in 24 years. He became managing editor of Money in 1980.

"He has been a major factor not only in business journalism but in the entire magazine industry," said Stephen B. Shepard, editor in chief of Business Week.

Photo: Marshall Loeb, left, is retiring as managing editor of Fortune magazine. He is to be succeeded by Walter Kiechel 3d. (Jack Manning/The New York Times)