Shortly after " 'night, Mother" opened at Arena Stage's Kreeger Theater, illness forced Ann Guilbert to drop out of what was in all respects a superlative production. Such occurrences are always unfortunate, but in this instance, it could have been disastrous.

Marsha Norman's Pulitzer Prize-winning drama has only two characters -- a daughter (played by Halo Wines), who at the start announces matter-of-factly that she is going to commit suicide; and her mother (Guilbert), who does everything within her limited powers to prevent the dread act from happening. Changing one of the actresses on short notice is bound to affect the dramatic equation.

Last week, Mercedes McCambridge stepped into the mother's role. And, indeed, " 'night, Mother," which continues through Dec. 8, is an altered production. Guilbert's performance was wiry, quick, nervous; her voice was sharp, edging up on a whine. As she found herself increasingly helpless to sway her daughter, she acquired the panic of an imprisoned bird. Her heart seemed to beat faster and her breath grew shorter. Guilbert dared acknowledge all that was ridiculous in the ineffectual, self-centered mother and that made her portrayal all the more wrenching.

McCambridge seems to have come at the character, who accurately describes herself as a "plain country woman," from another angle. She emphasizes the slowly accumulating bewilderment, the dull pain, the creeping paralysis. Her portly body and her deep, haunting voice seem to be tugged downward by gravity. Guilbert grew in animation until she had exhausted all her resources. McCambridge, a tragic actress, gathers hopelessness around her like a damp blanket. The only flutter is in her hands, as if they alone could stave off the inevitable.

The play remains an intensely painful chronicle of two people trying one last time to reach across the void that has separated them all their lives. But it has fewer peaks and valleys now. The humor is now gallows humor. The end is clearly in sight from the beginning. The drama is still there in all its meticulously humdrum detail, but it's thicker and darker without Guilbert's vivacity.

Wines continues to give a performance of such naked honesty that the daughter -- a drab nobody who failed to blossom -- is transformed in our hearts into the somebody she should have been. The actress is simply astonishing at depicting anonymity. She will make you cry for the waste and the want and the solace that never came.