Of George Bernard Shaw's 1919 work, director Harold Clurman wrote that ''there is a tendency to become solemn.'' Exhibit A: Robin Lefevre's current restaging. Granted, Heartbreak House (Shaw's favorite play) is an action-lite, dialogue-heavy Chekhovian homage. (Act 1: Make small talk; Act 2: Question everyone's moral fiber; Act 3: Reflect upon Acts 1 and 2 as bombs drop in the background.) But there's no shortage of Shavian wit, and while Swoosie Kurtz's clenched-jaw hausfrau is a kick, only Philip Bosco's grizzled Captain and Lily Rabe's sly Ellie have humor and gravitas. They're almost too good to be true.