Two circles, of eight students each, walk round and round, their bodies seeming to be pulled in two directions: Legs follow the circumference and torsos face the radius. Outside arms curve inward at waist level, as if resting along the back of a chair. Inner arms rise in a graceful arc, thumb and index fingers extended. All eyes stare intently into the center.

Staccato commands of "Wang Monkey," "Single Change," "Double Change," "Roc Bird" resound, and the orbiting stops. With surprising swiftness, legs pivot around, thighs together, feet pigeon-toed as arms swing out and a kick follows. In a blink the methodical walk resumes in the opposite direction.

This is pa-kua , an internal system of Chinese boxing for fitness and self-defense. The circular style is usually taught with a similar but linear boxing method, hsing-i . Central to all soft-style martial arts (another is t'ai chi ch'uan ) is a force called ch'i . When the mind and body's center of gravity shifts to the region below the navel - tan-t'ien - muscles and bones unclog and the ch'i flows freely. Liberated ch'i enables a small person to overcome a larger opponent.

Unleashing your ch'i takes a few years, according to instructor Bob Smith. Students of pa-kua/hsing-i find other rewards in their diligent practice that make the wait worthwhile - but don't expect literal explanations for their devotion. They are as subtle and elusive as the form itself.

For Suzanne Getz, a ceramicist who has been studying pa-kua for a year, it's an enjoyable exercise that increases her power of concentration and instills well-being.

"Pa-kua has its own momentum," says Anna Sofaer. After dabbling in yoga, aikido, folk dance and t'ai chi, she finds hsing-i and pa-kua the most satisfying movement arts because it has "a spiral movement of circles on circles that is both relaxing and freeing."

The boxing forms take on mathematical and philosophical tones for Warren Conner, a furniture builder who has been studying for six years. Conner says that pa-kua (and any movement art) reacquaints the body with an innate rhythm and the circles, ovals and curves found in nature and the universe.

Through relaxation, he says, the body regains an innate balance and sensitivity, and this in turn promotes flexibility.

Pa-kua's origins are appropriately mysterious. As tradition has it, it was in the mountains of Jiangsu Province where Dong Haichuan (of Hebei Province) learned the art from a Taoist who rescued him from starvation in the 19th century.

Hsing-i's origins are equally elusive. A noted 17th century boxer in Shanghai, Ji Longfeng, also learned from a Taoist monk he met in the Zhongnan Mountains. The two methods joined forces in the 19th century when hsing-i master Guo Yunshen (known as the "Divine Crushing Hand") fought pa-kua expert Dong Haichuan. The contest lasted two days with Dong defeating Guo on the third. Each impressed with the other's system, they agreed to teach their students both forms, a tradition maintained today.

The local pa-kua/hsing-i teacher, Bob Smith, says he is the first American to learn these forms. A judo black belt, former boxer and author of many books on martial arts, Smith worked in Taiwan as a civilian adviser to the Navy in the late '50s. His free time was spent studying with masters of every form from Shaolin temple boxing to t'ai chi.

"When I came back from Taiwan in 1962, I did some Shaolin but didn't feel like jumping around and kicking anymore," said Smith, whose primary devotion for 20 years was to judo. "Judo is no good after about 35. My back is lousy, really lousy from taking all those falls for students up into my 40s."

So Smith started t'ai chi, hsing-i and pa-kua classes. "You can practice soft forms your whole life, well into old age" he says. "Hard forms are just too wearing."

Effective as soft forms are, Smith doesn't teach them with fighting in mind. There's little contact sparring in his classes, because "It proves nothing." But if you want immediate results, Smith recommends taking a hard form like karate, kung fu or Shaolin boxing. "If I were going into a rough area, I would rather use judo, but it's not quickly learned."

There are scores of places to learn the basics of self-defense in the Washington area. But a growing number of women feel that because these are developed and practiced by men, they require a certain level of physical conditioning that women generally do not have. The D.C Women's Self-Defense Karate and Ja Hsin Do Academy are two schools teaching methods geared to women.

"Women are not socialized to let out their aggressions and clobber an opponent," says Carol Middleton, who runs the D.C. Women's Self-Defense classes. "They don't have the speed and strength, especially upper-body strength, to be effective."

Forms that emphasize competition and contact sparring, says Middleton, are intimidating to female novice. Many hard-style classes start off the first class with 70 pushups, when few women can do a dozen at the start. Instead of palm thrusts or wrist locks, she has selected karate techniques such as kicks because women have five times as much strength in their legs as in their arms.

But to learn any method successfully, Middleton insists, women must first overcome the notion that it's good to be weak. The next step is to accept pain and be able to think about injuring someone if ncessary.

Though her classes are taught with women in mind, Middleton welcomes men who shy away from the macho atmosphere in other schools: "I'm afraid the students might miss something if it were only female. The men in my class are also interested in practical self-defense."

Ja Shin Do founder and instructor Dana Densmore says women are her first priority because they're weaker than men.

"Most women develop best in the beginning with other women, because they feel safe enough to develop calm confidence about sparring," says Densmore. "Sparring is a place to learn to be skilled, calm and fight cooperatively with partners and learn control without worrying about injury. I have never found men to be safe in sparring. They often injure their partners."

Central to Ja Shin Do's philosophy is cultivating "self-belief mind," which Densmore says can prevent the paralyzing fear or rage that many women fall prey to when attacked. It instills an awareness that helps to sense and avoid potential confrontations before they can occur.

"A common problem with partially trained women is that they don't move with inner confidence or they may have a chip on their shoulder," says Densmore. "This can bring about an antagonistic response from a potential assailant."

Ja Shin Do, Densmore says, teaches an adaptation of a style learned from a Korean martial arts master, Kim Dong Pil. The "body shake," which he used but was unable to teach, was incorporated into the Ja Shin Do method and distinguishes it from other martial-arts styles. Described as a power theory that mobilizes the whole body's muscle systems in a coordinated action, it is effective enough to give a small woman the presence of mind and physical knowhow to deal with a much larger assaillant - providing that she could not foresee the situation and avoid it.

But to Densmore and her students, Ja Shin Do is a way of life that has helped turn their lives around. Densmore says she is no longer her own worst enemy, besieged with irrational fears about life in general that keep her from forming her own goals and concentrating on them.

To Bob Smith, learning a martial art gives one the confidence to say no to a fight. The cardinal rule his instructors imparted to him was that the purpose of learning the arts of battle is to firm one's self-esteem enough to get out of any situation with face: "It teaches you to run with confidence." CAPTION: Picture, THE WANG MONKEY, ONE OF THE MOVEMENTS IN PA-KUA. By Carol Conn.