Despite suffering from throat cancer the playwright Harold Pinter is to appear on stage next week in a new drama attacking militaristic politicians.

His agent, Judy Daish, yesterday confirmed that the writer of The Birthday Party and The Servant, who was once a heavy smoker, had recently been diagnosed with cancer of the oesophagus and was undergoing chemotherapy. "He feels well enough to work and is in good spirits," she said.

Pinter, 71, who has a brooding, magnetic presence on stage, will play an authoritarian presidential figure who spouts martial language reminiscent of the new, post-September 11 politics in Press Conference, one of two sketches he has written for a season of his work at the National Theatre in London.

He has long been a scourge of American militarism and the British politicians he claims are eager to do their master's bidding.

Both performances of the 45-minute monologue, next Friday and the following Monday, were long ago sold out. Only one of the eight other sketches, starring Corin Redgrave, Patrick Marber, Catherine McCormack and Frances de la Tour, is new.

Pinter is also currently directing his masterpiece No Man's Land at the National's Lyttelton Theatre and was looking well when he turned up a few days ago at the neighbouring Cottesloe to watch Henry Woolf perform his play Monologue.

His illness comes as a time when much of his work has attained the stature of modern classics, with The Homecoming starring Pete Postlethwaite sold out at the Royal Exchange in Manchester and the highly anticipated revival of The Birthday Party about to be performed at the Crucible in Sheffield.

Born in east London, Pinter has been a fearless fighter on behalf of some unpopular causes. Had not his writing brought him international recognition after the success of The Caretaker 40 years ago, he would have probably carved out an equally illustrious career as an actor.

Like his fellow actor/writer Steven Berkoff, who followed him, Pinter has a gift for menace, last seen on screen when he played a demonic crime boss in Jez Butterworth's Mojo.

A fanatical cricketer, he lives in Notting Hill, in west London, with his wife the writer and critic Lady Antonia Fraser - the daughter of the late prison reformer Lord Longford.