I AM sure that if Paul Keating succeeds in his ''threat'' to make Australia a republic, Her Majesty's reaction will be similar to that of her ancestor King George III when the United States became independent. He wrote to Lord Shelburne that he felt less unhappy about the dismemberment of America from his empire in the knowledge ''that Knavery seems to be so much the striking feature of its inhabitants that it may not be in the end an evil that they become aliens to this Kingdom.'' C. G. BILHAM Jardine's Lookout