David Mamet's two-acter, "A Life in the Theater," treats backstage pedantry and onstage rivalry between two actors young and old. Starting as a clash of innocence and experience, it develops as a gradual turnabout that makes for a fair play.

A series of brief scenes puts the actors in the dressing room and in front of the footlights, their backs to the audience at the Round House Theater. These amusing histrionics come from film and television as well as from the stage: parodies of war movies and soap operas, plus takeoffs of Williams and Shakespeare.

But as directed by Jerry Whiddon with David Cromwell playing mentor to Gerry Paone, matters never come to a head. Cromwell and Paone clearly expend a lot of energy as they don and doff costumes, act and chat -- but it seems energy loosely aimed. Their scenes peter out more than pay off, and what is supposed to be Paone's growing dominance over Cromwell seems abrupt and artificial when it comes.

This is too bad, because the two have their moments, especially in Act I. Cromwell, the vain and windy journeyman, and Paone, the shy, nervous beginner, achieve an occasional chemistry, as when Cromwell asks with pointed politesse -- "In our scene tonight, could you perhaps do less?" -- and the ever-hyperactive Paone looks crushed.

In the end, though, the older actor seems to have passed on nothing to the younger one but stagy affectations. A LIFE IN THE THEATER -- At the Round House through March 27.