Dramatic, zestful Dance Theater of Harlem in London

Giselle as a freed black slave in post-American Civil War days? Hanging Spanish moss instead of the expected autumnal leaves? Farm boys and girls collecting a sugar-cane harvest instead of the traditional peasant grape-picking celebrations?

This is the Dance Theater of Harlem's very different conception of a favorite time-honored ballet that was recently given its world premiere here.

The company will be performing the ballet in New York's City Center when its season opens in September (and - minus ''Giselle'' - it was the closing attraction at the Olympic Arts Festival in Los Angeles.)

This classical ballet company has been on a three weeks tour at the Coliseum Theatre in Charing Cross Road and has scored a resounding success with its program of 13 very different works, including the new ''Giselle,'' all intelligently staged and beautifully and differently presented.

The company last visited London three years ago and is one of this capital's favorites. Only two of this season's productions had been seen in London before, and the five ''mix and match'' programs played to capacity audiences.

What sort of fare tempted the London balletomane? Just one evening's banquet produced these differing pieces:

* Balanchine's ''Square Dance,'' where blue-leotarded ballerinas in pointe shoes neatly performed a balletically classical version of the American folk dance with strong, happy partners and a caller in blue jeans, cowboy hat, and red neckerchief who sang out his commands of ''promenade all'' and ''keep your eyes on Eddy'' to the strains of Corelli and Vivaldi.

* ''Wingborne,'' a barefooted pas de deux which featured superb dancing, careful partnering, and flowing rhythms by Yvonne Hall and Lowell Smith.

* ''Fall River Legend,'' opening with a blasted oak, lowering skies, and a gallows, showed the arresting dramatic face of the company in a performance of the tale of Lizzie Borden.

Karen Browne in the title role was riveting. The focal point whenever she came on stage, she became totally absorbed in the drama and won the sympathy of the audience who witnessed the mental cruelties she had to endure that finally drove her to the infamous killings.

* ''Firebird'' returned the audience to classical ballet. This production, with John Taras's choreography, took the story out of its familiar Russian setting to an exotic imaginary tropical jungle.

Stephanie Daubney was sensational as the Firebird - twitching, pirouetting at top speed after the prince of evil, usually known as Katschei, and with her final flutterings that rippled her whole body from feathered crown to trembling feet.

Such evenings showed the company's versatility and joyful approach to dance and the special contribution of both to the drama of the production.

The orchestra, under Milton Rosen-stock's baton, set off at a brisk pace, and when the blue velvet curtains were raised, they revealed not the wooden chalet of Silesia but a pillared Southern plantation, ''Madame Berthe's farm, Plaquemines Parish, Louisiana.''

The townsfolk, in sun-drenched yellows, oranges, and tans, stood chatting together beneath the hanging moss outside Giselle's home.

This Creole Giselle was based on research done by the founder and director of Dance Theater of Harlem, Arthur Mitchell, who discovered, while visiting southern Louisiana, similarities between legends of freed blacks of the area and that of the German peasant girl.

Southern social customs of the mid-1800s made it impossible for a young freed slave - Giselle - to marry into a black family which had received its freedom almost a century earlier.

The hero of this ballet, Albert, is, like the Albrecht of the original version, of a higher class than Giselle and knows in his heart that he cannot hope to marry her - even though he dresses like a freed slave.

Virginia Johnson in the title role was enchanting and spontaneous, a young girl full of love for life and dancing. Eddie Shellman was bewitched by her youthful beauty and her innocent love for him.

The first act poured forth like sweet molasses, exuding the finest qualities of freshness, exuberance, caring, and a sense of community.

Carl Michell's sets and costumes were splendid: Mme. Berthe, like a homey Aunt Jemima, wore a turban, gold hoop earrings, and a figure-hugging frock. There were poke bonnets, big floppy bows in the hair, suspendered trousers, lackeys in pink jockey suits, and the multipastel frilly apron dresses of Giselle's friends.

The imperious Queen of the Wilis was danced by tall and stately Lorraine Graves, whose entrance bourrees - tiny running steps en pointe - seemed like clockwork.

The corps de ballet was dressed in thin ball gowns that hung about the dancers like the Spanish moss on the trees. They fluttered eerily in a breeze from an off-stage fan.

The precision and neatness of the corps needed more polish (we have just had the Cuban ballet here, which set terrific standards) but the drama and atmosphere certainly did not diminish at all, and the production was a triumph.