Ballerina Martine van Hamel portrays the title role in Glen Tetley's new ballet, "Sphinx" - a creature half goddess, half human, winged, with the body of a lioness and the head of a woman. And the central dramatic dilemma of the role plays upon this duality, asking us to contemplate the struggle between divine destiny and human emotion.

It's no wonder Tetley chose her for the part; she seems ideally suited in her physical frame and artistic bent. There's something Olympian about her tallness and patrician bearing. On the other hand, the generosity of her movement and the cushioned sweep of her gestures bespeak an infinitely compassionate nature.

The assignment marks an important milestone in her career. Up to now in her development at American Ballet Theater - which presented the world premier of "Sphinx" last night at the Kennedy Center Opera House - the only role that has been specifically tailored for her has been one of the two female principals in Twyla Tharp's "Push Comes to Shove," which features Mikhail Baryshnikov as the male lead. In "Sphinx," Van Hamel has the chief role - Clark Tippet as Oedipus and Kirk Peterson as Anubis are her collaborators - and Tetley designed it for her, with her.

Having a major role created "on" oneself is a prime experience for any dancer. Van Hamel spoke about its meaning for her in a recent interview here.

"I've rarely worked in a first cast in ballet," she said, "and of course it's something I've always wanted to do. It's one thing to learn a role; it's another to actually become part of the creature process, to feel that a role is your own because it grew on you.

"As a dancer, you do create the part, in a way, even though the ultimate responsibility belongs with the choreographer. And Tetley has very definite ideas of what he wants and the kind of movement he's after. But I think my being there and being receptive, open, allowing him to find the shapes he wanted through me, was a part of the creative event."

The 25-minute ballet, which uses as its musical underpinnings Bohuslav Martinu's "Double Concerto for Two String Orchestras, Piano and Timpani," is lossely based on Jean Cocteau's play, "La Machine Infernale," written in 1943. The play is an imaginative extrapolation of the Oedipus myth, but Tetley has concentrated on the material of the play's second act, which depicits the metting of Oedipus and the Sphinx outside Thebes.

The Sphinx, attended by the jackal-headed Egyptian god Anubis, has been slaying all comers who failed to answer her celebrated riddle: What animal walks on four feet in the morning, on the two at noon and on three in the evening? But the love she suddenly feels for the mortal Oedipus softens her spirit. Against the alarms of Anubis, she gives Oedipus the answer - it is man in his three ages, infant crawler, upright adult and cane-assisted oldster - thus sparing his life and dooming her own.

"All of this is very abstract in the ballet," Van Hamel notes. "Tetley doesn't relate the story in realistic terms. I don't actually pose the riddle or give Oedipus an answer or anything like that - it's all conveyed in movement, in Tetley's way.But what he does show is the ambivalence of the Sphinx, her yearning for human love and her willingness to sacrifice herself for it."

Tetley's ballets most often tend to involve a large amount of sheer muscular exertion. Was this one an exception?

"No," says Van Hamel. "Glen's ballets are very challenging physically, and that's true of 'Sphinx,' though I do feel it's in no way out of my range. But what I particularly treasure about the role is that though the ballet is abstract, the Sphinx has a character, and she undergoes an emotional development, something happens to her. This helps one to keep a part alive to keep it from becoming a mere succession of steps - I know 'Sphinx' won't dry up on me."

It's hard to imagine any role drying up on this deeply committed artist, whose total immersion in the act of dancing is one of the salient traits of her performances.

The career of this Belgian-born dancer of Dutch parentage and international training has evolved steadily but slowly. Though she took a gold medal at the Varna competition in 1966 while she was still with the National Ballet of Canada (the same year Baryshnikov was a Varna winner), it wasn't until 1973 that she danced her first Odette-Odile in "Swan Lake" with ABT.

By now, however, she is recognized as one of the most individual and versatile of ABT artists, as persuasive as an ecstatically fresh Aurora in "The Sleeping Beauty" as she is in such contrastingly contemporary ballets as Tetley's "Gemini" or Ailey's "The River."