In the oddest twist of all in a story worthy of the Marx Brothers' farcical plotting, The Cocoanuts will finish its Off-Broadway run the way it started -- with Michael McGrath as Groucho.

Back when the show opened in June 1996 at the tiny American Jewish Theatre on West 26th St., The Cocoanuts starred McGrath, Peter Slutsker and Robert Sapoff as Groucho, Chico and Harpo Marx, respectively. The zany plot, by George S. Kaufman, and songs (including "Always") by Irving Berlin, clicked with audiences, and the show moved to the American Place Theatre in midtown, opening Aug. 15, 1996.

All was well until McGrath was cast in the Broadway revival of Once Upon A Mattress and wanted to take a one-week vacation before joining the new show, forcing the producers to either close Cocoanuts or find a replacement, fast. (Ironically, McGrath would later leave Mattress by mutual agreement. Double-ironically, Mattress is now having other troubles of its own.) Cocoanuts posted a closing notice -- but then rescinded it when Frank Ferrante, a Groucho expert, became available.

But now Ferrante is slated to direct and star (as Max Prince) in Neil Simon's Laughter On The 23rd Floor at Philadelphia's Walnut Street Theatre, Jan. 11-Feb. 23. He also has a one-night-only Jan. 27, 1997 booking at the Walnut to do An Evening With Groucho.

McGrath, who has seemingly patched things up with Cocoanuts' producers, will return to the show on Christmas day, Dec. 25, and stay with it until it closes, Jan. 5. By then, Cocoanuts will have played 165 performances and 22 previews at the American Place Theatre. According to production spokesperson Mark Cannistraro, a national tour is in the works. Will McGrath be in the tour? Say tuned . . . For tickets and information on The Cocoanuts, call (212) 239-6200.

-- By David Lefkowitz