LEAD: If it requires a special kind of nerve to heckle a pope, the Rev. Ian Paisley has it. Mr. Paisley, a leader of the hard-line Protestants in Northern Ireland, last week disrupted a speech to the European Parliament by Pope John Paul II, who Mr. Paisley implied was somehow sympathetic to the Irish Republican Army.

If it requires a special kind of nerve to heckle a pope, the Rev. Ian Paisley has it. Mr. Paisley, a leader of the hard-line Protestants in Northern Ireland, last week disrupted a speech to the European Parliament by Pope John Paul II, who Mr. Paisley implied was somehow sympathetic to the Irish Republican Army. Almost as soon as the Pope began his speech in Strasbourg, France, Mr. Paisley, a member of the European Parliament, rose from his seat holding a poster saying, ''Pope John Paul II - Antichrist,'' and shouted, ''I renounce you as the Antichrist.'' Other members of Parliament snatched the sign away and threw papers at Mr. Paisley, who was then quickly ejected from the building. An unruffled John Paul continued his speech.