NEVIS MOUNTAIN DEW, by Steve Carter. Directed by Horacena J. Taylor; scenery by Wynn Thomas; costumes by Alvin Perry; lighting by Larry Johnson.

Presented by the Negro Ensemble Company.

With Frances Foster, Ethel Ayler, Arthur French, Graham Brown, Barbara Montgomery, Charles Brown and Samm-Art Williams.

At the Kreeger Theater, 6th Street and Maina Avenue SW, through June 3.

"I used to fill a room," says Graham Brown from his iron lung, looking out on his stage family through a mirror crocked at a 45-degree angle over his head.

He still fills a room and, what's more important, a theater. They all do, the members of the extraordinary troupe that opened Steve Carters "Nevis Mountain Dew" at the Kreeger Theater last night.

They are the Negro Ensemble Company, based in a dilapidated upstairs railroad car of a theater in New York's East Village. Somehow they have managed to survive for a dozen years under the leadership of writer-director-actor Douglas Turner Ward, producing plays and employing actors we might scarcely ever otherwise see. (The plays have included "The River Niger" and "Ceremonies in Dark Old Men." The actors-those, that is, who have gone on to establish names for themselves away from the company-have included Moses Gunn, Esther Rolle and Roscoe Lee Brown.)

It would be easy to dismiss the play they are now producing as the least rewarding feature of the evening, particularly in the wake of its melodramatic denouement, written in the manner of Lillian Hellman to the third power. But in the first and second acts, especially the first, when "Nevis Mountain Dew" is just mapping out its territory and introducing us to the people who live there, playwright Steve Carter offers a lush demonstration of his ear, his wit and his technical skill.

"You try to keep it secret from the public, but we all know you was woman once," says the free-swinging younger sister Zepora to her rigid, self-sacrificing older sister Everelda.

"With my back?" exclaims Zepora's boyfriend Ayton when called on to help move a TV set, "You want me to visit hernia village?"

The action hovers around the horizontal form of Graham Borwn as Jared Philibert, the head of an aristocratically minded West Indian family living in Queens, N.Y., in 1954. Reduced by polio to a life of trading witticisms with his friend Ayton and austere kisses with his wife, Billie, he keeps a whole household of hangerson almost as imprisoned in his iron lung as he.

Who but the Irish and West Indians can use words like"prevaricate" in everyday conversation? The florid Caribbean English of "Nevis MountainDew" is one of the play's outstanding pleasures, particularly as delivered by Frances Foster and Arthur French.

Foster, all pained innocence as she drops mischievous hints of her sister-in-law's infidelity, and suddenly full of cocky repartee when her famous fruitcake is slightly impugned, makes the utmost of the part of Everelda.

How she manages to get a huge laugh from the single word "chunk" with a question mark attached (when a visitor suggests he will try a chunk of her cake) is a mystery, but it could hardly be a more delightful mystery.

Foster also is notable for the expansive, calculated but entirely believable manner in which she uses her arms. The whole company, in fact, exhibits a similarly confounding blend of lightspiritedness and formality in its acting.

The title refers to a brand of rum that arrives in a case at the beginning of the play and is gradually consumed during its course. "One drink, you see the future!" proclaims Charles Brown as Lud (still another thickly entertaining performance).

The literalness of that observation-the rum helping everyone face up to the future-is just one sample of the melodramatic hokum that gets the better of the play as it heads toward its finish.But it is a pleasure to watch these actos even when they are handling hokum. CAPTION: Picture, Graham Brown and Barbara Montgomery, by Harry Naltchayan-The Washington Post