When the Dance Theatre of Harlem appeared at the Kennedy Center Opera House a year ago this month, it took no time at all to recognize that the troupe, after a dozen years of struggle, had graduated to the rank of a major international ballet company.

Last night DTH returned to the same hall to begin a week's visit, once again as part of the Dance America series, and swiftly reconfirmed its stature. It's a vibrant, often dazzling, brilliantly trained entourage with a style and youthful energy all its own, and as its individual dancers grow year by year in artistry by measurable strides, so too the ensemble as a whole gains commensurately in character and authority.

Part of the excitement of the company, and a natural corollary of its youth, is that it is still in the process of defining itself, especially in regard to repertory. Co-founder and director Arthur Mitchell was himself molded by George Balanchine, and Balanchine has been the principal formative influence since the early days of DTH, supplying both bedrock ballets--like last night's "Serenade"--and the neoclassical orientation which remains the backbone of DTH dancing.

In recent seasons, however, Mitchell has been steering the repertory towards dramatic ballets of diverse origin--last year's winning "Scheherazade," from the fabled Diaghilev era, was a prime example. This year has brought several new essays in this direction, two of which were introduced to Washington last night--a very impressive restaging of "A Streetcar Named Desire," Valerie Bettis' 1952 dance version of the celebrated Tennessee Williams classic; and John Taras' new version of Stravinsky's "Firebird," which is visually and physically flamboyant enough to prompt cheers from the audience, but which nevertheless seems fairly anemic as a ballet composition.

"Streetcar" remains, as a play, one of the most profoundly poetic and deeply registered of American dramas. The Bettis dance version is something else--it's a kind of danced musical, in the tradition of Ruth Page's "Frankie and Johnny," Balanchine's "Slaughter on Tenth Avenue," and Jerome Robbins' "Fancy Free," to all of which it bears a family resemblance. The intimate tragic resonances of the play aren't there, except fleetingly--they were functions of Williams' script. What the ballet does have is immensely pungent characterizations, a vivid and savvy, if unoriginal, dance language, and an expertly serviceable score in a jazz vein by Alex North. It all adds up to a beautiful piece of dance theater, which DTH has assimilated with characteristic pizazz.

Virginia Johnson is superb as Blanche, the fragile belle with a sordid past whose quest for redemption is crushed in the brutal hands of Stanley Kowalski, her cloddish, Neanderthal brother-in-law. Her lissome delicacy is utterly right for the role, and she's consistently convincing throughout the painful stages of her undoing.

Brawny and athletic Lowell Williams makes a fine foil as Stanley, projecting both his cool cynicism toward Blanche and his impetuous ferocity with equal skill. Also excellent are Elena Carter as Blanche's benign sister Stella, and Donald Williams in the complex role of Stanley's sensitive friend, Mitch. The portrayals are admirable right down to the most ancillary characters; these DTH dancers appear to have an instinctive theatrical canniness that "Streetcar" elicits to the full. Peter Larkin's sets and Saul Bolasni's costumes powerfully evoke the play's steamy atmosphere.

The chief virtue of the new "Firebird" is the chance it gives lovely Stephanie Dabney, in the title role, to show off her supple extensions, mercurial phrasing and luminous spirit. Geoffrey Holder's decor and costumes transfer this Russian fairy tale of a magic bird who defeats the forces of evil and unites the royal lovers to an exotic jungle ambiance. The concept's okay, except that it's out of key with both the score and Taras' eclectic, derivative and ultimately dull choreography. And why the monstrous "Creatures of Evil" should look like oversize butterflies is anybody's guess.

The performance of "Serenade" was much less overtly dramatized and "interpreted," and hence more severely classical, than last year's; it was fascinating to see how much better the noble romanticism of the choreography was served by this approach. The fine principals were Virginia Johnson, Lorraine Graves, Elena Carter, Eddie Shellman and Lowell Smith.