Geeks & Geezers: How Eras, Values and Defining Moments Shape Leaders. (Bookshelf).

By Warren G. Bennis and Robert J. Thomas. Harvard Business School Press, 221 pages. $26.95.

No less than Peter F. Drucker calls this "Warren Bennis' most important and his most enjoyable book." It is a bit different from some of the many books written by Bennis, the founding chairman of the Leadership Institute at the University of Southern California: It tries to identify qualities of leadership by looking at two very different generations to examine commonalities and differences.

Written with Robert J. Thomas, a senior fellow with Accenture's Institute for Strategic Change in Cambridge, Mass., the book sets up the two classes quite simply: "geezers" are recognized leaders who are over 70; "geeks" are aged 20 to 35, and would be young enough to be grandchildren of many of the geezers. None of the geeks are yet household names, though some are likely to be in time, while the geezer list has many prominent names in industry and the arts -- architect Frank Gehry, newsman Mike Wallace, former basketball coach John Wooden, stockbroker Muriel Siebert.

The differences are considerable, the authors write. The geezers experienced the Depression and World War II and were more "conventional," with working fa-thers, stay-at-home mothers and widespread prejudice against putting wo-men in upper management. Geeks, on the other hand, are far more skeptical about large organizations and eager for more responsibility earlier in their careers -- yet, paradoxically, far more interested in finding "balance" in their work and private lives. It's instructive that, in a table comparing the two classes, 8 percent of the geezers' parents had divorced, but 44 percent of the geeks' parents had.

Not surprisingly, the list of geeks is populated with technophiles, many of whom hold high-tech positions or started online ventures -- like Geoffrey Keighley, a 24-year-old who founded Gameslice, a video game industry Web site, or Sky Dayton, a 31-year-old who helped found Earthlink and Boingo Wireless.

So what ties these disparate generations together? Bennis and Thomas argue that leaders have all been through what they call a "crucible," a defining event or series of events. They write: "Era, individual factors, and certain key competencies -- adaptive capacity, above all, but also the ability to engage others through shared meaning, voice and integrity -- often coalesce around a critical experience of event to shape leaders." It is in these crucibles that "existing values are examined and strengthened or replaced, where alternative identities are considered and sometimes chosen, where judgment and other abilities are honed."

The book features illuminating interviews with members of the two generations, sketches of individuals and overarching lessons that marry with the stories and interviews. One of its conclusions, not surprisingly, is that the geeks believe that employees need "vision," and are far more interested than earlier generations in being placed in leadership roles and not being subservient to a hierarchical form of leadership. Clear articulation and observance of an organization's core values are also crucial to these young managers, whose favorite writers include individualist champion Ayn Rand.

Geeks and Geezers is a thoughtful, often trenchant, important book that should stimulate discussion about how leaders are molded and how different generations share, reject or shape prevailing values.