The Actor's Studio's month-long celebration of the Group Theatre begins Jan. 27 with a evening addressing on the origins of the famed 30's troupe and featuring an array of celebrated actors.

The event will take commence at 7 PM at the Actors' Studio (432 W. 44th St.) with a film about the Group Theatre. Arthur Penn's official welcome will be followed by a short film of Phoebe Brand, 91, an original member of the Group.

Actor David Margulies will then read from Group founder Harold Clurman's plan for the company. Reading from The Brookfield Diaries- journals kept by the Group's members during the theatre's first year--will be actors Ellen Burstyn, Ruben Blades, Roscoe Lee Browne, Stephen Lang, Angelica Torn, Rip Torn, Gene Saks, Sondra Santiago, and Susan Strasberg.

Blades and Tovah Feldshuh will follow the diaries with a song from Johnny Johnson, the only musical the Group ever staged. Wendy Smith, who wrote a history of the company, will then speak. Joanne Woodward and Helen Krich Chinoy will close the evening by leading the audience in a discussion about the company.

The festival continues through May 17 with a variety of play readings and symposia. For information and reservations, call (212) 944-9444. -- By Robert Simonson