Combining the energy, enthusiasm and rhythm of dance routines with muscle-toning calisthenics, aerobics now is beginning to secure a place for itself in the realm of competitive sports.

According to figures released by the National Sporting Goods Association in 1988, approximately 24.5 million Americans are involved in aerobics.

But what began as a simple health club activity in the early 1980s has taken on serious competitive overtones. There are currently 17 competitions in the United States each year. International competitions have included participants from as many as 17 countries.

More than 200 men and women were at White Marsh Mall near Baltimore this weekend for the Mid-Atlantic regional competition of the annual Reebok National Aerobics Championships. Finals in mixed pairs and team competition will be held today starting at 10 a.m. All of the competitors are shooting for spots in the national finals to be held early in 1991.

More than 12,000 have competed in this national tournament since it's inception seven years ago. The competition format, which includes men's and women's individual divisions, a mixed-pair category and a classification for teams of three, stipulates that competitors perform a three-minute routine to the music of their choice and will be judged on skill (60 percent of the total score) and presentation (40 percent of score).

The skill portion concentrates on strength, flexibility, form, safety and selection of exercises. Each program must include four pushups, four jumping jacks, four high leg kicks and four abdominal curls. Presentation is based on creativity, showmanship, musical selection and interpretation and appearance.

According to Greg Blair, an aerobics instructor from Timonium, Md., who took first place in the men's individual division in last year's Mid-Atlantic competition, the judges also look for innovative moves. "They want to see how the audience reacts to your routine," he said, "and they like to see each person or pair come up with their own 'signature' moves."

Blair, who again is competing in the men's individual division this year, also will team with Susan Tyndall of Millersville, Md., in mixed pairs. According to Blair, synchronization is most important in pairs and team competition. "The key is to get a partner {or partners} who is equal to you in strength," said Blair. "The judges will be looking to see if your kicks are the same height and if you and your partner perform the moves with the same ability."

This is the second year Blair and Tyndall will compete as a team. They finished second in last year's competition. Blair thinks they've learned more about each other's skills and styles during the past year.

"Susan had to work on her strength and one-arm pushups and I had to increase my flexibility," he said.

Along with the increasing popularity of aerobics and the availability of aerobics videotapes has come serious concerns. Aerobics has found its way into the living room, and there have been debates about the effect of high-impact exercise on the joints, the effectiveness of low-impact workouts and, generally, the safety of at-home workouts.

Blair says the home workout should be approached with caution. Those who are new to exercise should probably sign up for a supervised aerobics class to learn the basics of conditioning before starting a program of their own.

Although both high- and low-impact aerobics provide good cardiovascular results and muscle toning, low-impact moves reduce stress on the back and joints because they involve keeping one foot on the floor at all times.