It may not be the most relaxing way to spend leisure time, but the exhilaration of skydiving keeps Paul Hentzen coming back for more. ''You just can't beat that kind of freedom,'' says Mr. Hentzen, of Wichita, Kan. With classic understatement he adds, ''It doesn't appeal to everybody.''
While other people spend a sunny afternoon in the pool or catching a game on TV, Mr. Hentzen takes advantage of the clear skies. ''Skydiving is mainly a weekend sport (for me),'' he says. ''It's very seasonal and works around the weather. In good weather I can make as many as 10 jumps a day.''
Mr. Hentzen, a remodeling and restoration contractor, has made over 500 jumps since he began skydiving as a junior in college six years ago. He earned his pilot's license in 1979 and owns a plane with one of his brothers, who is also a pilot. Mr. Hentzen is in the process of building a plane, which is about half completed.
''In Wichita to be interested in airplanes is second nature,'' he explains. ''It's the center of the aviation industry.''
Leisure-time activities run the gamut from the adventurous to the contemplative. Working people devoted to a special pursuit in their off hours find it removes them from the everyday routine and helps renew their energies.
New Englanders and others across the country are discovering orienteering, a sport popular in Europe. At orienteering meets, competitors are given a map and a compass. The object is to complete a given course on foot or on skis in the shortest time possible, punching a card at various checkpoints along the way. Different courses are geared to beginners and more advanced competitors.
''It's a real challenge,'' says Margo Thornton, a member of the New England Orienteering Club based in Boston. ''Orienteering is not just navigating and it's not just running. It's a combination of the two.''
Courses generally take approximately an hour to an hour and a half to complete. ''It depends on how fast you run and how lost you get,'' she says, laughing.
Last summer, Miss Thornton placed first among the American women at the collegiate world championships held in Czechoslovakia. Now that she is out of school and working full time as a state environmental engineer, she runs about 50 miles a week for training and competes nearly every weekend during the peak seasons in the spring and fall. This month she placed second in the women's division of the US team trials, qualifying her for the world championships in Hungary.
Many working people are involved in informal community athletic clubs. David Witherbee of Concord, Mass., is a founding member of the Concord Runners, a group that meets every Saturday morning at 8 o'clock for a six-mile run through wooded trails.
''It started with three of us about five years ago. We kept inviting people and now we have a list of about 30 members,'' says Mr. Witherbee, who is a financial planner. ''There is a tremendous camaraderie, and it improves our running.''
During the warmer months he also participates in canoe racing, which involves some additional workouts. ''I usually do some exercises, work with weights, and then go out and paddle hard,'' he says.
Other ambitious leisure-timers pursue less rigorous but equally absorbing activities.
On a muggy Saturday afternoon in Washington D.C., chances are that Dawn Hill and her husband Hal will be working in the garden they transformed from an empty lot next to their townhouse.
''It's really fun, and it occupies about 50 percent of our time in the summer ,'' says Mrs. Hill, a home-based professional calligrapher.
Last year the couple rented the 15-by-60-foot lot, which they later bought, and cleared the area of debris. ''It was a real lesson in urban archaeology,'' she says. Today they and seven other green-thumbed Washingtonians cultivate a profusion of flowers and vegetables.
Bessie Harris, a speech and language pathologist in Santa Fe, N.M., was part of the cast for a soap opera now under consideration as a series for a cable station. Once the pilot was completed Mrs. Harris continued working with members from the cast in a group called the ''Canyon Road Actors.'' The ensemble performs established and original works at the Armory of the Arts in Santa Fe.
Mrs. Harris, who is married to an artist and is the mother of two children, also finds time to head a Girl Scout troop for handicapped girls. Two years ago she wrote a grant and submitted it to the Professional Women's Club of Santa Fe. The group agreed to fund the troop. For the girls' activities, Mrs. Harris adapts the regular Girl Scout badges to help teach troop members community ''reference skills'' such as how to use a library, go to a restaurant, or go to a film. She is currently looking for an organization to help fund a similar program for boys and girls.
In the San Francisco Bay area, Jim McCutchen has joined the ranks of moonlighters. By day, he is a management and budget analyst for the Santa Clara County Transportation Agency. After hours he is the program director for KFJC, a new wave and alternative-music radio station in Los Altos Hills.
''I'd been listening to the station for some time,'' recalls Mr. McCutchen. ''Two years ago I decided I'd like to get involved.'' With no previous media experience or training, he landed a job in the public affairs and news department. He moved up to become the news director and was recently promoted to program director. His responsibilities add up to 30-plus hours a week on top of his regular job.
''A lot of personal time has been usurped, but that's the choice I've made,'' says Mr. McCutchen. ''What I do in my leisure time other people would consider work. But I find the fact that I don't depend economically on [my second job] removes the slave aspect from it; I can do it for pure enjoyment.''