"Action was never your forte, was it?" goes a line in director Sam Mendes' enthralling new "Uncle Vanya." Though the words, in Brian Friel's invigorating translation, are articulated by one of the play's minor characters, the question might have been posed by modern audiences to Anton Chekhov himself.

The contemporary complaint about Chekhov has to do with a certain histrionic inertness. Far too often these days, productions of his masterpieces do the work of over-the-counter sedatives. Worshipful directors and actors check into the stifling rural estates of the playwright's imagination and can't locate the keys to anything but melancholy and ennui. Or, conversely, they find only eccentric humor in the squabbles and insecurities of the groping members of the households.

While Chekhov's skills as a psychologically astute observer of human behavior have never been seriously called into question, the cumulative effect of all these dreary, hothouse-flower treatments of his plays has been to erode confidence in his ability as a storyteller. There are only so many times that you can sit through something stuck in idle before you begin to waver on the talent of the manufacturer.

Which is why Mendes' "Vanya" is a landmark event. Over the course of 2 hours and 45 minutes of flawless, vibrant theater, Mendes eliminates all doubt about the viability of Chekhov. To watch this "Vanya," with a cast so in sync and in balance that you could swear they'd spent a lifetime together at a dacha, is to experience Chekhov at full throttle, with all the anguish and irony and desperation intact.

Mendes, the Oscar-winning director of "American Beauty," made this play and "Twelfth Night," with which it's running in repertory, his valedictory productions for Donmar Warehouse, the eclectic London theater company he headed from its establishment in 1992 until this past December. He's brought the two works to the Brooklyn Academy of Music for a nearly two-month run, a visit that further solidifies BAM's position as the most significant and adventurous venue in the nation for theater from Britain and continental Europe. As to why a top-rank troupe like Donmar does not include the capital in its itinerary, Washingtonians can only curse the fates (that is, after hopping a Metroliner and scrounging for seats at BAM's Harvey Theater).

A mere dozen actors -- including the classical stage sensation Simon Russell Beale and the cinematically in-demand Emily Watson -- constitute the repertory company for these two sprawling dramas. What Mendes does with them, particularly with "Vanya," demonstrates a level of dramatic savoir-faire exceeding even the fine ensemble work in both of his motion pictures, the visually arresting (though overpraised) "Beauty" and last year's moody "The Road to Perdition." (He also directed the current Broadway revival of "Cabaret" and is staging a new "Gypsy" this spring with Bernadette Peters.)

Indeed, this "Vanya" may be the most accomplished Chekhov I've ever experienced. The achievement begins with Beale's shattering Vanya and extends to a passel of portrayals endowing the familiar characters with identities as distinct as fingerprints. It's a play all about suffering, from the loneliness of lovelorn Sonya (Watson) to the guilt-driven alcoholism of Dr. Astrov (Mark Strong) to the perpetual cynicism of romance-starved Yelena (Helen McCrory).

In such intelligent hands, despair is not a drag. In scene after scene, the actors reveal the layers of the play, the complexly detailed instances of hysteria, suppressed passion, comedy. The bare stage is simply decorated -- a long wooden table, a piano, a carpet of Persian rugs -- and you're repeatedly reminded how symbiotically these characters share it.

Vanya's discovery, for example, of the attraction between Astrov and Yelena, the woman with whom Vanya is almost comically in love, makes for a wonderful convergence of tragedy and farce. It begins with the heat of the moment in which Astrov shows Yelena some maps of the area; in a nifty prelude to a kiss, McCrory's Yelena surreptitiously drinks in Astrov's smell.

Beale's poignantly constant Vanya, who has devoted a thankless lifetime to the upkeep of the estate and the nourishment of futile dreams, walks in on their embrace, and you feel as if you catch in Beale's eyes the switching off of a light. Rarely is a stare so filled with meaning; the actor stands there, frozen, a statue of dejection. In Beale's fierce gaze you get so much: the sense of Vanya's failure, the idea that he knew all along that this was coming, the notion that more humiliation may be in store.

This is confirmed in the heart-piercing scene to come, in which Vanya's brother-in-law, the snooty, self-consumed academic Serebryakov (a superb David Bradley), announces his plan to sell the estate. No matter how many times you may have seen the play, the explosion in helpless fury by Beale's Vanya may reduce you to a blubbering fool. He becomes the instrument for all of the barely contained outrage in the world aching for a voice.

"Vanya" is such a sustained achievement that "Twelfth Night" is bound to feel like a lesser one. Distinguished by some terrific performances, among them Beale's Malvolio, Bradley's Andrew Aguecheek and Anthony O'Donnell's Feste, the production is nonetheless far less persuasive than the Chekhov. Mendes' version emphasizes the more sinister aspects of the play; in other words, it accentuates not the whimsical, gender-bending love story of Viola (Watson) and Orsino (Strong) but the torture of Malvolio at the hands of Sir Toby Belch (Paul Jesson) and Maria (Selina Cadell).

Dark is the more fashionable shade these days for "Twelfth Night"; it's the tone Trevor Nunn also adopted several years back with his movie version of the play. Some of Mendes' choices are questionable, such as having actors continually pose in a life-size picture frame whose purpose never comes completely into focus.

Watson, however, always does. The actress, who received Oscar nominations for "Breaking the Waves" and "Hilary and Jackie," is a generous performer. Her soulful Sonya gives "Uncle Vanya" its humane core, and her smirky Viola is an appealing linchpin for "Twelfth Night." It's fun, too, to connect the relationship dots between the two works. Strong plays the objects of her affection in both dramas; in both, too, the women Watson portrays are active creatures in all but matters of the heart. Sonya and Viola, interestingly, must both patiently await the judgment of the men they fancy.

Still, it's the work of Watson and company in "Vanya" that cuts to the emotional quick, that leaves you lightheaded and sated. Most of the time, productions of Chekhov simply talk at you, and talk some more. Here is one that speaks to you.

Uncle Vanya, by Anton Chekhov and Twelfth Night, by William Shakespeare. Directed by Sam Mendes. Sets, Anthony Ward; costumes, Mark Thompson; lighting, Hugh Vanstone; music, George Stiles; sound, Paul Arditti. With Luke Jardine, Cherry Morris, Gary Powell, Gyuri Sarossy. Each production approximately 2 hours 45 minutes. Through March 9 at the Harvey Theater, Brooklyn Academy of Music, Brooklyn. Call 718-636-4100 or visit www.bam.org.

Simon Russell Beale shines in both "Twelfth Night" (shown) and "Uncle Vanya" at the Brooklyn Academy of Music, both directed by Sam Mendes.