Producers have wasted no time booking the Cort Theatre for springtime, after its smash run of David Hare's The Blue Room. General manager Albert Poland's office confirmed that producers Ric Wanetik and Frederic Vogel are bringing in a new play, Marlene, for an opening April 11, 1999.

Production spokespersons for Marlene were out of the office for the Christmas holiday, but according to a source close to the show's casting office, Sian Phillips, notable for her London credits, has been cast as the lead: Marlene Dietrich. Phillips took over for Rosemary Harris in the Broadway run of An Inspector Calls.

Two other roles are still being sought: Vivian, Dietrich's personal assistant and fan, and Mutti, a concentration camp survivor and friend to the teutonic actress-diva.

Sean Mathias will direct Marlene, which starts rehearsals March 8, 1999. Mathias' last Broadway assignment was the Kathleen Turner starrer, Indiscretions, in 1995.

Dietrich's film credits include "The Blue Angel," "Witness For The Prosecution," "Touch of Evil" and "Judgment At Nuremberg."

Those seeking personal reminiscences, good and bad, of Dietrich can catch producer Alexander H. Cohen's solo, Star Billing, Off-Broadway through Jan. 4.