Hard at work in an employee dining room at Yellowstone National Park, S.P. Lee, 79, dishes out a steady stream of jokes, banter and good cheer along with the scrambled eggs and fresh fruit he serves to his groggy fellow employees filing in to start their day.

Chuckling heartily, the retired tax lawyer from Apache Junction, Ariz., acknowledges that some people might view his summer stint as a short-order cook and food server as the "lowest job on the totem pole," but Lee says it has allowed him to have a lot of fun in a beautiful place and changed the way he views himself.

"It's the first time in my life that I've been able to be myself, to be an extrovert," Lee says, explaining that in his former career as a lawyer, he was compelled to put on a sober and dour face to win his clients' confidence. "I'm laughing more than I ever have."

Lee is at the forefront of a new group of aging workers, living longer, healthier, more mobile lives, who are redefining retirement by finding new jobs and new lifestyles in some of the nation's most scenic vacation spots. At Yellowstone National Park, once almost entirely staffed by college-age workers, about 20 percent of the workforce today is older than 50.

Recruiters for Amfac Parks and Resorts Inc., the Denver company that operates the park's hotels and restaurants, are combing recreation vehicle trade shows, holding job fairs in Sunbelt cities and advertising in newspapers to find more of them.

"We found the population of our typical entry-level worker, age 18 to 24, had decreased, and in order to stay alive, we had to start to turn over the rocks to find other employees," said Julie McCluskie, director of human resources for Amfac, which also operates park concessions at the Grand Canyon, the Everglades, Death Valley and Bryce Canyon, Utah. "We started to realize there was this resource at the other end of the age spectrum."

In 1997, about 12 percent of the workforce, or about 3.9 million people, was 65 or older in 1997; by 2006, this age group is expected to make up about 15 percent of the workforce. The percentage of working seniors is expected to grow even more dramatically in the following decades, either by choice or due to financial necessity. A study issued early this year by the Employee Benefit Research Institute found that 80 percent of baby boomers said they intend to keep working at least part-time after age 65 -- a sharp contrast to the 22 percent of Americans aged 65 to 69 who are working today.

"I don't like to go to a senior citizen center," said Dottie Hillman, 79, of Billings, Mont., who works summers at Yellowstone in the accounts payable department. "They're all old people there."

Meanwhile, the number of younger workers has declined 14 percent during the 1990s because of the birth dearth following the post-World War II baby boom. Management consulting firm Watson Wyatt Worldwide projects that the shortfall of younger workers will last for 40 years.

This generational shift is clearly visible at Yellowstone, where older workers are being employed, housed and fed side by side with younger workers, chafing at each other's presence at some times and cheerfully collaborating at other times.

"A lot of companies are just waking up to it," said Howard Weizmann, managing consultant in Watson Wyatt's Washington office. "We're used to having two or three generations in the workforce, and now we are going to have four generations or even five generations. But these intergenerational issues -- while you can deal with them -- are very real."

Ski resorts, river barges and white-water rafting companies, traditionally the exclusive domain of young workers, are actively recruiting seniors, mostly to fill customer service positions, using the "Older and Bolder" page of the Web site www.coolworks.com. Bill Medove, for example, recruiting manager at the Mammoth Mountain ski and golf resort in California's Sierra Nevada, said 200 of its 2,000 employees are older than 55 now, up from a handful in the early 1990s.

Medove said senior workers are especially good at handling situations that require extra finesse, such as redirecting young people who are snowboarding recklessly.

"They're not confrontational; they're diplomatic," Medove said. He added that the company has found that older people are often more conscientious. "That 18-year-old kid doesn't care about guest service or food quality," he said.

The U.S. Army Corps of Engineers manages 450 lake projects nationwide, most with campgrounds, and about half of these sites are now supervised by senior citizen couples who bid for the right to work there and collect user fees on the agency's behalf. Similarly, about half the employees working at the 500 campgrounds affiliated with Kampgrounds of America Inc. (KOA), are senior citizens, said Mike Molthop, general manager of the St. Petersburg/Madeira Beach KOA Resort in Florida.

"It appears this is on the rise," Molthop said. "A lot of people are retiring at earlier ages than before, and they are not ready to kick back. They want to travel, have experiences, have fun, look for things to do."

That's the kind of whirl that Wanda Harris, 58, of Austin, has in mind. In 1996, she sold her electrolysis studio and went to work at the Summer Olympics as transportation coordinator for the equestrian venue near Atlanta. When her husband, Don, a newly retired state meat inspector, came to pick her up, she told him it was time to hit the road.

Since then, the Harrises have been semi-nomadic. First they went to Flagg Ranch Resort near Jackson Hole, Wyo.; then to Glacier National Park in Montana; then to Shenandoah National Park in Virginia, and then on to the Mammoth Mountain resort in California. Wanda usually works at the front desk or gift shop and Don drives a van to transport guests or employees.

Until recently, many resort companies spurned older workers because there were plenty of eager young people to hire, in a world where age discrimination remains common.

But Amfac officials decided that hiring older people could be advantageous. Tim Baymiller, Amfac's director of human resources at Yellowstone Park, said having a large senior workforce helps the company make more money because it has allowed Amfac to extend the tourist season from May to September, instead of limiting it to June through August, when college students are available.

"And for reliability, you can't beat the commodity you are getting there," he said.

Tourists at Yellowstone said the presence of so many senior-age workers improves customer service. "They are more willing to go out of their way to make your stay pleasant," said Joe Tharpe, of Florissant, Mo.

One reason the seniors like Yellowstone so much, despite pay of only about $6 an hour, is that Amfac provides a variety of housing, from collegiate-style dormitory rooms shared by two resident workers to recreational vehicle sites to small apartments. It also offers three meals a day at employee dining halls similar to the one where S.P. Lee presides over the grill and skillet. Room and board costs $8.75 a day, paid through payroll deduction.

The older workers more easily take the good with the bad. National Park Service ranger Sam Holbrook, 67, a retired high school science teacher, loves conducting geyser-walk tours at the Old Faithful Visitor Center each summer.

He is unfazed when asked to handle jobs younger workers view as demeaning, such as scraping bird droppings off the bicycle rack outside the center. "You just learn: When something's got to be done, you get in there and get it done," he said.

But Holbrook and many of the older workers acknowledged they can resist taking direction at times. He said that when he got his job evaluation last year from his boss, who is in his early forties, the supervisor remarked with irritation that he had the same mild criticisms he had voiced a year earlier, and that Holbrook hadn't changed.

"I said, `When are you going to learn?' " Holbrook recalled with a laugh. `I'm not going to change.' " A moment later, Holbrook reflectively added, "Sometimes you get set in your ways. That's the problem with being an old guffer."

Another dilemma: Many seniors like to be home when the sun goes down. Irene Passfield, 64, who works as a hostess at the Roosevelt Lodge and fills in as a horse wrangler on the Old West Cookout dinner, told her supervisor she was willing to work long hours and pitch in to cover other positions when co-workers didn't show up, but she wouldn't accept an evening shift. "I said, "I don't work at night,' " she recalled.

Her husband, Bill, 67, a former construction industry manager who drives the stagecoach on the Old West Cookout, nodded. "Old folks are hard to manage. They've been there, done that."

Another problem is that some older people simply can't handle the physical labor some jobs entail.

But younger workers pose problems, too, usually stemming from arrogance or alcohol, Baymiller said. Some, he said, think every night is a party and fail to make it to work because they have hangovers or oversleep.

Mostly, the multi-generational workforce gets along pretty well, said both older and younger workers, and come to have a deeper understanding of each other's problems, joys and woes. Greg Love, a 30-year-old summer breakfast cook, said he'd made good friends with one co-worker in his seventies who came to Yellowstone to work the summer after his wife died. At first, the man spent much of his time alone fishing, Love said, but he gradually began socializing with the young people.

"He's laughing with us," Love said. "He's got some stories. And he doesn't mind having a little Old Granddad with us."