WHAT ARTHUR Mitchell and the Dance Theater of Harlem have accomplished is nothing less than the eradication of a deeply ingrained cultural myth. If a black dancer is hereafter denied entrance to a classical ballet troupe, the reason can no longer be any alleged unsuitability by reason of ethnic traits or proclivities. The evidence of the DTH standard of rigor in the classic style is irrefutable, if any such evidence were ever needed.

The troupe, here this week in two ambitious programs at the Carter Barron Amphitheater, arrives at a peak moment in its eight-year evolution. Last November, the company gave a second command performance for England's Queen Elizabeth, the first command performance ever televised. The company has played to capacity houses in Norway, Mexico, Belgium, Finland and Berlin. And the company's successful public television special of 1973 had a sequel this year in a segment of the "Dance in America" series, which showed the dancers both in rehearsal and performance.

Make no mistake -- a demonstration of feasibility, such as DTH has provided, is one thing; reversing a tide of white bias or indifference that was centuries in the making is quite another. As recently as the mid-40s, Janet Collins, one of the very few black ballerinas ever to achieve white recognition -- she was premiere danseuse of the Metropolitan Opera Ballet for four years -- was turned down in auditions for the Ballets Russes because of her skin color. She was told at the time that either special parts would have to be invented for her, or that she'd have to paint her face white.

At this moment, neither of the country's largest, most prestigious ballet troupes -- the New York City Ballet and American Ballet Theater -- has a single black member above the rank of corps de ballet, and there are precious few even in that category. A sprinkling of black artists, most of them male, can be found in smaller metropolitan and regional troupes.

If one inquires why there are so few blacks in the field, the answer often comes back that it's hard to find adequately trained candidates. Undoubtedly. Ballet has traditionally been a white art in every way, and it has always been linked to white concepts of comeliness, nobility and reserve which were purported to be alien to black culture and physique. Ballet training is long and expensive, and nothing resembling an "affirmative action" program for recruiting blacks into ballet schools had ever been undertaken by established institutions.

Arthur Mitchell set out to counter those factors with the creation of DTH. Mitchell himself, in a brilliant career as a dancer, had been so conspicuous an exception as to shake the foundations of the myth beyond ignoring. As a principal of Balanchine's New York City Ballet, he didn't appear in "black" roles; his Puck in "A Midsummer Night's Dream," or his solos in "Agon," for example, were triumphs too purely classical to be construed as anything else.

Mitchell gave up his performing career at its zenith, because he felt a debt of conscience to coming generations of black youths who might not be as lucky and intrepid as himself. The DTH began strictly as a shoestring operation, with a handful of students working in an abandoned garage. It has since evolved into the first internationally renowned black ballet company and a flourishing school which has trained more than 3,500 youngsters, not just in ballet but in every other area of dance expression, including jazz, modern dance and the black African heritage.

Classical ballet, to Mitchell, is a means to a variety of ends. In its most classical manifestations, traditional ballet found room for Spanish, Hungarian, Italian, Chinese and other "exotic" idioms without qualm. Why not, then, the contemporary styles of black vernacular dance, or the folk, religious and ceremonial legacy from Africa?

The company's Carter Barron programs reflect this diversity of aims. There are items mirroring the glittery imperial past of ballet, such as the "Corsaire" pas de deux, and Balanchine's "Allegro Brillante." There are dramatic, romantic and lyrical pieces in a range of moods, such as a "Romeo and Juliet" pas de deux by Gabriella Taub-Darvash to the music of Prokofiev; William Dollar's "The Combat," with its chivalric imagery; Royston Maldoom's "Adagietto," set to Mahler; and William Scott's playful "Every Now and Then." There's Mitchell's own classic abstraction, "Holberg Suite," in the Balanchine manner. And there are works which fuse ballet technique with the beat, tempo and movement signatures of the modern Afro-American spectrum, such as Talley Beatty's "Caravansarai," Geoffrey Holder's "Dougla," and Louis Johnson's "Forces of Rhythm."

The irony of the black effort to crack the ivory curtain of classical ballet in the United States is that blacks have contributed to the dance culture of the United States to a degree far out of proportion to their numbers. Since the first appearance of black slaves, whites have been quick to imitate, adapt and transform the steps, rhythms and shapes of their dances.

A very great proportion of the dances which have been the rage of our ballrooms, night clubs, concert stages and musical shows were black in origin, from the Cakewalk of the plantations to the flappers' Charleston to the jazz routines that pepper the ballets of Balanchine and Robbins and give them their "American" stamp. For a variety of reasons, blacks have had a much smoother time making their way in the domain of modern dance, and in this field, the names of black dancers, choreographers and company directors are legion. But in a recently compiled directory of black dance units across the nation, issued by the periodical Dance Herald and containing some 90 entries, only two fall into the classical category -- DTH and Washington's Capitol Ballet.

Ballet is the last resisting stronghold. Besides Arthur Mitchell, there have been and are individual black dancers who have made the grade in the ballet establishment -- John Jones, Christian Holder, Keith Lee, and Sylvester Campbell are some who have had enduring careers in recent times. The significance of the Dance Theater of Harlem is that it shows that these artists cannot be dismissed as freaks of nature, and that if only the soil be watered, the flowers will spring forth. That the seeds -- black men and women of talent -- have always been there cannot be rationally doubted.