LONDON (AP) _ After winning a Tony in his first crack at Broadway, Nigel Hawthorne is giving the performance of his life in ''The Madness of George III.''

The 62-year-old actor, known to followers of TV's ''Yes, Minister'' and ''Mapp and Lucia,'' had critics straining for tributes after the Nov. 28 opening of the Alan Bennett play.

From the opening scene where he survives an attempted stabbing by a minion armed with a dessert knife to later illness-induced verbal ramblings, the actor offers an incomparable study in royalty gone to ruin.

Dressed for most of the play in a nightshirt as doctors bleed him and induce sweating in their search for a cure, Hawthorne makes a bumptious yet savvy figure at his wisest when seemingly most deranged.

If the scenario occasionally recalls ''King Lear,'' playwright Bennett makes the link explicit. In the second act, George III leads a recitation of Shakespeare's tragedy, clearly aware of himself re-enacting the tragedy.

It took almost 200 years for medical historians to discover that George III's ''madness'' was in fact porphyria, a genetically transmitted condition characterized by abdominal pain, hypertension, psychosis and discolored urine.

Thus, Bennett's creation is the poignant victim not only of medical ignorance but of his foppish son (Michael Fitzgerald) who can't wait to ascend the throne.

Folded into the story are satiric touches that are vintage Bennett, who last addressed the royal family when he dramatized Queen Elizabeth II in his 1988 play ''A Question of Attribution.'' (The play was screened this year on British television, with Prunella Scales repeating her stage role as her majesty.)

This George III calls his German queen (Janet Dale) ''Mrs. King.'' Bennett pokes fun at politicians who outstay their welcome, making the Whig statesman William Pitt (Julian Wadham) and his plea for ''five more years'' sound suspiciously like Margaret Thatcher.

There are also references to the American Revolution - from the British view one of the disasters of George's reign. One of George's first signs of distress is a spasm while speaking the word ''states'' (as in United States), and a similar incident near the end indicates that his apparent recovery was not to last.

In an interview, Hawthorne said this role was the most demanding of his career.

''It was an opportunity to incorporate a lot of qualities I have as an actor: the manic side, the absurd side, also the ability to be emotional,'' said Hawthorne, whose role as the love-struck C.S. Lewis in ''Shadowlands'' on Broadway demonstrated his ease at playing emotional extremes.

Bennett said in an interview that he was aware of rewriting history.

''The stock English liberal historian's view is that George III was mad because he stood in the way of constitutional reform and was a Tory,'' said the playwright, who majored in history at Oxford.

''I think more and more that's really been deconstructed in a way. ... He was called 'farmer George,' so therefore it was assumed he was a rural, rustic fool. He wasn't that at all. He was quite sophisticated.''

Bennett is accustomed to writing about real people. In addition to his play about the queen's encounter with the former spy Anthony Blunt, Bennett has written both a play and a separate TV film about author Franz Kafka as well as a screenplay (''Prick Up Your Ears'') about the subversive playwright, Joe Orton.

Last year, he intended to write a play about the novelist Kenneth Grahame and ended up adapting Grahame's much-loved children's classic ''The Wind in the Willows,'' also now in the National repertory.

Is history writing easier than starting from a blank slate? Bennett isn't sure.

''You can take what people know, and that is very useful dramatically on stage,'' he said in his distinctive Yorkshire accent. ''On the other hand, 18th-century politics are so different to politics today that you've got somehow to feed that into the text, and that's quite hard.''

He said he'd like to be able to tell the audience, ''Come half an hour earlier. We'll just go through the basics we're going to use, and then we'll cut them out of the play.''

''The Madness of George III'' is scheduled to run at least through June at the National's Lyttelton auditorium. It is selling well despite mixed reviews, boosted no doubt by Bennett's stature and by unanimous acclaim for Hawthorne.

Might New York beckon? Hawthorne is wary, knowing that the Broadway production of ''Shadowlands'' flopped.

''I'm not sure this would go in New York,'' said Hawthorne, who found himself stopped nightly on Broadway at the stage door by TV admirers of his foppish Georgie Pilson in ''Mapp and Lucia'' and the scheming Sir Humphrey in ''Yes, Minister.''

''It might be too wordy, too parochial, too British.''