AS the Irish Repertory Theatre's most artistically successful season to date draws to a close, artistic director Charlotte Moore and producing director Ciaran O'Reilly won't be basking in all the well-deserved accolades. The final play of the Rep's season opens this week, and plans are already afoot to host their 20th anniversary celebration with cocktails, dinner and entertainment at the Pierre Hotel on June 9.

"Because its our 20th anniversary we're bringing a lot of our company members back to perform pieces from some of the hit shows we've had," says O'Reilly.

"We've staged productions of Finian's Rainbow, The Streets of New York, and The Irish and How They Got That Way by Frank McCourt. We'll also stage an extract from Grandchild of Kings featuring Ciaran Sheehan (the Irish tenor who has sold out shows at Carnegie Hall)."

The Rep's annual fundraiser is always a celebrity-studded affair, but - in keeping with New York tradition - the stage and screen megastars who turn out each year to support the theater usually only confirm their attendance the day before the event.

"We'll have multi-Tony Award winners like Frances Sterne Higgins and Marian Seldes and many others," says O'Reilly. "The format will be like a cabaret with music and singing, with perhaps a bit of drama too."

Meanwhile, the final play of the Rep's 20th season, Prisoner of the Crown by Richard F. Stockton, will bring the brief but brilliant life of Irish patriot Sir Roger Casement to the stage when it opens this week.

Born in Kingstown - now called Dun Laoghaire - in Dublin in 1864, Casement was one of the brightest stars of the British consular service until he gained an international reputation for his humanitarian efforts in the Congo and later in Peru, exposing the forced labor the natives were subjected by the agents of colonial rubber companies.

Casement's reports created an international sensation, which resulted in his knighthood. With his passion for social justice, inspired in part by the democratizing lessons of his discreetly closeted homosexual life, he was one of the world's first great humanitarians in the modern sense.

Retiring from the British consular service in 1912, he became involved in Ireland's struggle for independence and was rewarded for his efforts in very typical colonial fashion by being disgraced and then hanged for high treason August 3, 1916.

O'Reilly, who's directing the show, said, "It's a play based on the trials of Roger Casement, as seen throw the jury. The cast of eight plays over 49 characters including the defense and the prosecution. I thought I knew Casement's story but I realize now I knew nothing. He lived the most exciting and complex life."

Like many people in Ireland, thanks to the conservative nature of our school system, O'Reilly had heard in a vague way that Casement's name had been sullied by his trial, but he was quite unaware that the Irish patriot had been gay.

"I have leaned about the extent of his involvement, how central he was to the fight for Irish independence. In his early years he had excelled beyond anything that had been expected of him," says O'Reilly.

"He was sent to the Congo to be British colonial officer, send reports on activities, and keep an eye on things. He went far beyond that. He sent extraordinary reports back, often taking his life into his own hands in the process. He would take his life into his own hands, and he'd write about what he saw. That was a brave man."

In Prisoner of the Crown Casement finds himself in a familiar dramatic setting for so many Irish patriots - giving a speech from the dock. Just as they had with the famous Irish dramatist Oscar Wilde, the British establishment had become adept at playing to popular prejudice to rid themselves of their most eloquent critics.

Casement was sentenced to be hanged, just a few short years after being knighted, for treason in what was called the trial of the century. All he had accomplished for both the Empire and the fledgling Irish Republic had been forgotten; being gay, he had no legacy and no country.

Prisoner of the Crown is now playing at the Irish Repertory Theatre, 132 West 22nd Street. For tickets call 212-727-2737. For tickets to the 20th anniversary celebration call 212-213-1166.