Al Pacino has played his share of thick- tongued toughs, and now he's at it again in the Kennedy Center's Terrace Theater, but one has to admit he's convincing. He's an asset in an already accomplished production of "American Buffalo," David Mamet's bitterly funny play about working-stiff machismo and helpless rage.

Pacino embodies both as a punk nicknamed "Teacher," while also projecting a pathetic vulnerability. In Mamet's perverse vision, he's the blue-collar -- or in this case, black-vinyl-jacketed -- answer to Walter Mitty, seeking thrills not in heroic deeds but in an act of petty theft. Such are the marvels of the endangered American-male ego.

Playing would-be mentor to Donny the junk dealer, who evokes a giant koala bear as portrayed by J.J. Johnston, Teach spouts words to live by like a foul-mouthed Dale Carnegie: "Take your shot," is a printable example.

At the same time, strutting to and fro like a frightened rooster, he's bully to Bobby the dope addict who sweeps out Donny's junkshop, played by James Hayden as a moist- eyed pup, and he's also his own worst enemy, tripping himself up at every turn.

The play is set in the junkshop, a few days after a customer has paid Donny the princely sum of $90 for a Buffalo nickel, with Teach and Donny hatching a plan to rob the fellow's house. Over two acts, with Bobby regularly blundering in, they haggle over the finer points of their criminal conspiracy, and consider its implications with the thoroughness of logicians. They talk about it, shout about it, and in the end, never do anything about it.

Mamet has an unerring ear for the way people talk and try to talk, and he has fun with dialogue from mundane to profane to ridiculous. For instance, there's a lengthy give-and-take between Teach and Bobby, pregnant with pauses, on whether it will rain ("It might," Bobby concludes) and a raft of pronouncements from Teach, with the following being typical: "Don, you have your job and I have my job. I'm not here to smother you with theory. Think about it." Not bad advice, where Mamet's concerned. AMERICAN BUFFALO -- At the Terrace Theater through September 25.