AN EVENING OF CHANCE ENCOUNTERS -- At D.C. Space through October 12. Call 347-4960 or 232-7210.

If you were weaned on Broadway and Kennedy Center fare, you might think it unseemly to climb a steep, narrow staircase and buy your ticket from an actor.

Settle into a metal folding chair in the dingy loft above the restaurant -- is this a show or a seance? God forbid there should be a fire! -- and you could conclude that nothing good can come of this.

But, as it turns out, "An Evening of Chance Encounters," the Spheres Theater Company's presentation of two American one-acts, has left little to chance. And despite rough spots, the company's productions of "Hopscotch" by Israel Horovitz and "Birdbath" by Leonard Melfi, both disturbing works from journeymen playwrights, are difficult to resist.

Known as the D.C. Space, the small house -- 55 chairs tightly drawn around a set, the noise of police sirens and down-shifting trucks wafting in from the street below -- is well suited for plays such as these: two-actor tours de force, encounters between misfit men and women that often assault the audience with terrible insights. The close quarters almost guarantee a visceral reaction, and that is what these plays demand.

This is true especially of "Birdbath," the second play on the program and the more successful of the two, both as a play and as a production. The play, which premiered off-Broadway in 1965, begins mundanely enough, with a waitress and a cashier closing up a New York greasy spoon for the night. But ultimately, as the setting changes to a one-room walkup, it builds to the blood-curdling intensity (excuse the mixed-medium metaphor) of the best of Hitchcock's thrillers.

Brian Hemmingsen, who also happens to be the company's executive producer, plays Frankie the cashier to Maureen McGinnis's Velma the waitress, and both turn in performances that aren't lightly to be quarreled with. As Frankie, a worldly-wise would-be poet given to swilling bottled martinis, Hemmingsen swings naturally between bluster and brooding, sarcasm and sentimentality, his protrayal only slightly marred by a penchant, a la Brando, for delivering certain crucial lines inaudibly.

As the lovelorn Velma Sparrow, terrorized (we deduce) by a domineering mother, McGinnis walks a nice fine line between simple-hearted frankness and dark neurosis. Her wavering voice and gestures, her eyes blank with fear even as she smiles sweetly (once the scene has changed from the restaurant to Frankie's seedy room, Hemmingsen screams savagely, "I'm sick of hearing about your mother") are all perfect for this character of birdlike fragility. McGinnis, in a word, is great.

Akim Novak's direction is intelligent and caring, right down to the left-over chili, dirty plates and subtle shifts in lighting, and he takes fine advantage of a difficult space.

"Hopscotch," the opening play, has its powerful moments, but is less satisfying than "Birdbath" -- as much because of the playwright as the production. Horovitz, who wrote it for a Paris debut in 1974, handles a meeting between long-lost lovers in a perplexing manner that mixes symbolism, polemic and Beckett-like absurdity, sometimes leaving the audience -- maybe the actors, too -- wondering what's going on.

The last line, "I never played hopscotch with you," uttered by the character Will/Earl to the character Elsa/Lorali, somehow doesn't bring it all together.

Still, Laurel Allen as Elsa/lorali, a sex-starved minister's wife, is spirited enough to hold one's interest, even if Robert Shampain, as her first love, back after a long absence from the Massachusetts town where they grew up, is often stiff and dry.

By way of warning, both "Hopscotch" and "Birdbath" are explicit in language and action, so you might want to leave the kids home.