SUMMIT CONFERENCE," a very black comedy by Glasgow playwright Robert David MacDonald, gets its area premiere in a sound staging by the New Arts Theater Company. In this second production by the company, Camilla David, founder and director of the fledgling group, again demonstrates painstaking care, from the slick set to the brave choice of brash material.

Set in 1941, MacDonald's feverishly funny play imagines a meeting between two of history's most infamous mistresses, Hitler's bored and restless Eva Braun and Mussolini's pampered Clara Petacci.

While their men are off in another room of the Berlin Chancellery, apparently plotting to invade Russia, the women, public scandals both, cagily circle each other, dropping coy euphemisms for war and atrocities, gossiping about American movie stars and the color of military uniforms.

The bizarre domestic situation swiftly assumes the exaggerated style of a political cartoon in a vicious parody of nationalism -- the two mistresses literally become Germany and Italy.

The clever device shows these very foreign countries as strange bedfellows, allies by necessity rather than choice. As the social visit wears on, with ample liquor and delirious conversation, the two become entangled in a scandalous clinch on the couch. Director David orchestrates the rapidly escalating and darkening volley of nasty political bitchery, punctuated with sly physical gestures throughout.

Whole hunks of the bristling dialogue seem to be paraphrased from Hitler's "Mein Kampf" manifesto. An essential part of a successful war, Eva explains, speaking in Hitler's voice, is finding a scapegoat. "I would encourage you to find a persecutable minority as soon as possible, by Christmas at the latest," she advises Clara, then demonstrates by intoxicating and humiliating her naive manservant, an attractive 19-year-old German soldier who seems to represent both the gullible German people and the Jews.

The two women/countries vulgarly seduce and humiliate the boy, forcing him to strip to see if he is circumcised. It's a cruel scene; it makes the actor and audience squirm, and it makes most immediate the terror of absolute power.

The cast does well with this strong stuff. Lora Tarantino, who resembles a young Lauren Bacall, plays Eva with wicked melodramatic menace, eyes widenening with fanatical zeal. As flip, chic Clara, Stephanie Correa is funny and deft with her slicing retorts. And Michael Russotto is affecting in the taxing role of the soldier. There is some difficulty all around with the German and Italian accents. The casting indicates nationality clearly enough, and the imperfect accents are a distraction, a stumbling block for MacDonald's caustic diatribes. SUMMIT CONFERENCE -- Performed by the New Arts Theater at All Souls Unitarian Church, 16th and Harvard streets NW. 654-8332.