As pop music pumped through the air, the wooden floor of the Wilde Lake Middle School gymnasium vibrated with the simultaneous slap of eight 36-foot, plastic jump-ropes, followed by the pounding of dozens of feet.

Suddenly, the rhythmic slapping-and-thumping stopped short. Giggles filled the air while several girls and boys untangled themselves from ropes covered with red, white and blue beads.

"This is getting too easy. We're going to add something," head coach Jim McCleary told the more than two dozen members of the travel team of the Kangaroo Kids Precision Jump-Rope Team.

The group took the addition of a new step in stride, continuing to practice choreographed routines for a recent halftime show at the Washington Wizards basketball game at MCI Center in the District.

Members of the team travel across the country giving demonstrations of jump-roping skills at schools, festivals and other events. In recent years, the group has performed at the White House, Walt Disney World in Florida, in European competitions and as far away as Australia.

They are the elite of the Kangaroo Kids, a nonprofit organization begun 21 years ago by a Howard County physical education teacher. Kangaroo Kids works closely with the Maryland affiliate of the American Heart Association to promote physical fitness through its demonstrations as a "Jump Rope for Heart" team. This fall, 65 children in kindergarten through 12th grade have signed up for Kangaroo Kids. Children need only know how to jump rope to join, but becoming a member of the travel team can take years of skill development. That includes learning such skills as jumping in tandem, performing complicated tricks in time to music and jumping over several ropes twirling simultaneously.

"Just about anything you can do with a rope, the kids will do," said Gaylen Euler, the organization's administrative coordinator.

A sport that requires spending only a few dollars for equipment, jump-roping is gaining in popularity around the globe, said Jean Hodges, a Kangaroo Kids coaches' adviser and a board member of the U.S. Amateur Jump Rope Federation, which was created in 1995 out of the merger of two national groups. In 1996, the Federation Internationale De Saute a la Corde was formed to serve as a world jump-rope organization. Twelve countries are now members.

"It's just getting very popular because it is an inexpensive sport, and it is a lot of fun," Hodges said. "There's a lot of variety. You can either do it with a group of kids or as an individual sport."

While the organization focuses on developing a jump-roper's aerobic conditioning and demonstration skills, many team members over the years have won awards in regional, national and international competitions that test speed, skills and creativity.

One is Amanda Ramsey, 17, a senior at Atholton High School, who has garnered numerous national and international awards. On Oct. 31, she took home a silver medal in the female master's single-rope competition at the International Rope Skipping Federation's World Jump-Rope Championships in St. Louis. By winning the medal, Ramsey is ranked the second-best female athlete in the world in single rope jump-roping, according to McCleary.

Ramsey, who also plays volleyball and lacrosse, said there's no mystery why she never bothered to hang up her jump-rope as most of her classmates did years ago.

"I just really like it. It's a really unique sport. It makes me unique," she said. "The competition aspect is the best part. You get to travel everywhere."

Teammate Jim McCleary, 17-year-old son of coach "Mr. Mac" McCleary, also has won his share of awards. Honored as the top male jump-rope athlete at the 1997 Amateur Athletic Union Junior Olympic Games, he won a bronze medal at the St. Louis competition, where jump-rope athletes from 10 countries and Puerto Rico competed.

Jim McCleary, who joined Kangaroo Kids when he was 3, admits that he used to take his share of ribbing in elementary and middle school because of his passion for jump-roping. But once he started winning competitions, his friends' attitudes began to change.

"It's a different skill not everybody has," said McCleary, a senior at Long Reach High School.

Developing the jump-roping skills needed to get on the Kangaroo Kids travel team or to compete takes hours of practice. Members of Kangaroo Kids are divided into different groups according to skill level, and each practices several hours a week at Wilde Lake Middle School in Columbia. Travel team members also sell pizza and cookie dough and hold other fund-raisers to raise money for their trips.

"It's hard work," acknowledges Coach McCleary, a county physical education teacher who spends four afternoons each week coaching the Kangaroo Kids. But it is definitely worth the sweat and concentration necessary to master the intricate jumping sequences, say travel team members.

"It gets you energetic. It feels really good to learn something new," said 10-year-old Emily Butterfield of Columbia, a Kangaroo Kid for six years and travel team member for three.

Being a member of Kangaroo Kids does more than build strong leg muscles; it also helps foster self-esteem, especially in children who may not have the aptitude to play other sports, Euler noted. "You don't have to be a super athlete to jump rope," she said. "The most wonderful thing about Kangaroo Kids is that those kids who wouldn't otherwise have the opportunity to shine are able to do it."