The pope can sing, but can he dance? As it happens, Sunday, Oct 7 -- the day Pope John Paul II, about whose vocal accomplishments we have heard much lately, conducts a solemn mass on the Mall -- has just been named Arthur Mitchell Day in Washington by proclamation of Mayor Barry. The honoring of Mitchell, in recognition of his contributions as a maker, teacher and missionary of dance, was announced last night from the stage of the Warner Theatre by Peggy Cooper, chairman of the D.C. Commission on the Arts and Humanities.

The occasion was the opening of a three-week engagement of the Dance Theatre of Harlem, the troupe founded 10 years ago by former New York City Ballet star Mitchell, who directs the company with his longtime colleague, Karel Shook.

What the opening-night performance demonstrated resoundingly was that Mitchell, Shook and the DTH are deserving of the highest honors possible for artistic achievement. The DTH has always been, since its earliest years, a kind of wunderkind among classical ballet troupes, a prodigy. But even in its peak periods, even as recently as its last Washington visit in 1977, the company seemed ever a bit mightier in its ambitions than in its attainments.

One's admiration tended to be tempered, if only subliminally, by a certain sense of reservation: The troupe was astonishing "considering" -- considering its youth as an organization, the struggles it weathered, the special obstacles it confronted and so forth.

Last night made it unmistakably clear, however, that in the two short years that Mitchell has had in which to reconstitute the troupe after a wave of dancer "defections," he and the troupe have outdone their own best past efforts.

Mitchell has been saying lately that his "new" company is better than the old one ever was, and he's right. What we saw before us at the Warner last night was a ballet company of the first rank, and one with a unique identity and personality. This is the case, moreover, without any provisos. The dancers and apprentices performed with a cohesion, refinement, energy and dance intelligence that are the marks of the ballet elite, and though there were three works new to Washington on the program, even the familiar choreography looked newly born and vitalized.

Among the evening's many happy surprises, none was more electrifying than the first Washington showing of Mitchell's own "Manifestations," created in 1976 to a coruscating expressionistic score (somewhat in the vein of Varese) by a young Chicagoan, Primous Fountain III.

In a stringently stylized manner, and freely mixing classicial and modern dance idioms in a fashion reminiscent of Glen Tetley or Maurice Bejart, Mitchell lays out the tale of the Garden of Eden in "Manifestations" (the title is a bit of a mystery).

Unlike Tetley or Bejart, however, Mitchel manages to convey the story clearly, simply and without pretension or erotic vulgarity.In so doing, and with the help of a dazzlingly inventive but spare dance vocabulary, the choreographer also transmits the elemental and scorching power of the Biblical allegory -- the ancient contest between good and evil, the corrupting force of fleshy lusts.

Toward these ends, Mitchell requires but three dancers -- Adam (Eddie Shellman), Eve (Stephanie Baxter) and the Snake (Mel Tomlinson), who makes his eye-boggling entrance dangling precipitously from a "vine" lowered from the top of the stage. The dance portrayals by this DTH trio were nothing short of shattering.

Also on the program, the first of four, the troupe will present in the next three weeks, was Mitchell's "Holberg Suite," looking more graciously contoured than ever before; a splendidly bravura "Corsaire" pas de deux; an uneven but hypnotically ritualistic "Doina" by Royston Maldoom; and Robert North's "Troy Game," which afforded the DTH men a field day for witty histrionics and virtuosity. Lydia Abarca, Virginia Johnson, Elena Carter, Yvonne Hall, Mel Tomlinson and Ronald Perry were among the dancers who made a particularly strong impression throughout the eveing.