Mr. Howe and Mr. Strauss define the youngest Americans reaching adulthood, whom they call millennials, as those born since 1982, not yet out of college. Others date the generation from 1977, when births began climbing after a decade of declines. In either case, a generation is shaped more by cultural experiences than strict demographics, and it is clear in many offices that those under, say, 25 represent a different wave. Last month, the Army changed its recruiting slogan after 20 years from ''Be All You Can Be'' to ''An Army of One,'' to appeal to the individualism of the younger generation.

Jokes about Gen Y in the workplace are surfacing, including some on a Web page (http://members .home.net/j2cbat/ritalin.html) that offers tips for ''dealing with the Ritalin generation.'' These include posting ''speed limits in hallways'' and ''preparing for vacation time to be accrued in nanoseconds.''

''Be flexible,'' managers are cautioned. ''Attention levels in the Ritalin generation may be so vastly improved that psychic abilities might be awakened. Don't be surprised if your assistant asks you to sign a letter to someone you don't know, dated months in advance.''

It is easy to divine the roots of the divide: while Gen X'ers came of age in an era of soaring national debt, predictions of Social Security apocalypse and a bleak job market in the recession of the early 90's, the younger set mostly has memories of economic expansion. Add to this that their parents, the baby boomers, were obsessed with child rearing and car-pooled their progeny to soccer games, tutoring and community service projects to beef up college résumés, and self-esteem, and you have a generation that expects the world at 22.

For many 30-somethings in a position of managing the new kids on the block, there is wide resentment. Mr. Lundy, who is the executive director of marketing and strategic planning at Esquire, remembers the recession years, when Gen X'ers took dead-end McJobs, or were grateful for any entry-level professional work. He is surprised to see young colleagues bristle at small tasks.

He recalled asking an assistant to walk a few blocks to deliver vital documents to a client, but the assistant refused. ''It was extremely urgent that the client got it right away,'' Mr. Lundy said. ''We're at 55th and Broadway, and the client's office was at 49th and Sixth. When I asked my 22-year-old assistant to run over there, she responded, 'Why are you asking me to do this?' ''