Just when the summer theater doldrums were beginning to set in, the Keen Company comes through with a smart, well-acted revival of the 1964 docudrama “In the Matter of J. Robert Oppenheimer.” Carl Forsman’s ambitious new production gets so many things right – the casting, the staging, the McCarthy-era atmosphere – that its excessive length can be overlooked.

Drawn from actual transcripts of Oppenheimer’s 1954 appearance before the Atomic Energy Commission, Heinar Kipphardt’s drama came out of the postwar German Theater of Fact, a documentary theater movement that culled morality plays from voluminous official records. Kipphardt documented the so-called “father of the atomic bomb” in his battle to keep his security clearance in the midst of American anti-red hysteria. The tension is that Oppenheimer, an arrogant iconoclast, wouldn’t apologize for his political opinions – even when it came to associations with Communism.

Historically speaking, Kipphardt’s highly selective version of events is rife with convenient oversimplifications. (Oppenheimer him self criticized the play, snorting that “the whole damn thing was a farce, and these people are trying to make a tragedy out of it.”) But in dramatic terms, “In the Matter of J. Robert Oppenheimer” is a remarkable piece of theater.

In Nathan Heverin’s sleek, crisp set design, Oppenheimer sits facing the audience on the stage level, either in the witness chair or on a nearby settee. Behind him, white men in suits fill ranks of risers, all facing the audience. Closest to Oppenheimer are his two ramrod straight, snarling prosecutors; then come his defense attorneys, humanists with slumped shoulders. In the back row are his jurors – three non-physicists, solid citizens handpicked by the government to pass judgment on his loyalty.

With a roomful of suits sitting at conference tables with pencils and water glasses, the play could easily feel like watching C-SPAN, but Kipphardt’s deft handling of the material – and the power of these character actors – make it more akin to watching “Twelve Angry Men.” The progression of witnesses for and against Oppenheimer (including fellow scientists Edward Teller and Hans Bethe) gradually fleshes out a world, at the center of which stands one mercurial, elusive, irresistible figure – Oppenheimer himself.

The talented character actor Thomas Jay Ryan makes a believable, robust Oppenheimer. “I don’t like to think the thoughts of others,” he snaps at one point, and his lawyers squirm every time he indulges in his pet arguments. Though his ego may be his undoing, he’s dazzling.

Mr. Ryan lets Oppenheimer’s rapid intellect shine through his quick connections across disciplines and eras, and gives glimpses of his lightning quick wit. He shows Oppenheimer’s certainty of being liked in a confident little boy grin that says, “Aren’t I clever?” And his blood clearly boils when he’s forced to suffer fools as witnesses against him, or when his interlocutors can’t grasp his meaning.

As crafted by Kipphardt, Oppenheimer is the central figure on whom the play’s hopes rest – a man who chose Hiroshima as a target but had “terrible moral reservations” about building a hydrogen bomb 10,000 times more powerful than the one America dropped there. Oppenheimer – the bomb maker – wants disarmament talks, and used to be a “fellow traveler” of his Communist friends. He insists on his right to keep his “pink” friends and his security clearance; indeed, by his definition, the America he serves so loyally is founded on the belief that his private opinions are his own inviolable right.

But in its 2 1/2 hours, the play starkly elucidates the trade-offs between personal freedom and national security. Wherever you come down on Oppenheimer’s clearance – or the Patriot Act, for that matter – the intellectual and moral territory of national security is a thorny issue, as “In the Matter of J. Robert Oppenheimer” makes plain. Was Oppenheimer a “traitor,” as one prosecutor argues, because he dragged his feet on creating the hydrogen bomb while the Soviet Union forged ahead, terrified of building a weapon that could wipe humankind off the face of the planet? Or was he simply a man with a conscience?

Such distinctions were often treated like philosophical poppycock in the witch-hunt atmosphere of the McCarthy era, and “In the Matter of J. Robert Oppenheimer” makes palpable the frustration of being a reasonable man in a room of belligerent dogmatists. “Yes or no!” the prosecutor barks, when the question itself is a trap. Under the bright white lights, Oppenheimer resists the very framing of the issues, but to no avail. He is a physicist, and while debate, experimentation, and philosophy are part of his scientific community, in this official chamber, any deviation from bland conformity is evidence of anti-Americanism.

Mr. Ryan’s superb portrait of Oppenheimer is supported by the fine character work of the strong ensemble, including compelling performances by Dan Daily, Steve Routman, Jonathan Hogan, and Matt Fischel. The ensemble energetically shoulders the text-heavy play, even when carrying it makes their steps a little unsteady, and Mr. Forsman’s production would benefit from even further judicious trimming – especially in the strangely anti-climactic final minutes.

Yet something about the very redundancy of the testimony summons an Orwellian sense of drowning in bureaucracy. “In the Matter of J. Robert Oppenheimer” is vividly reminiscent of a time when people had a greater horror of war, a keener terror of repression, and a sharper fear of innocuous-seeming committees.

Until June 27 (220 E. 4th Street, between Avenues A and B, 212-868-4444).