London — Just when hopes had been rising for a new period of peace for Northern Ireland, violence and threats from both Catholics and Protestants are putting new and urgent pressure on London and Dublin. As Britain and Ireland continue backstage efforts to come up with new ideas for an ultimate solution to decades of religious strife:
* IRA gunmen board a British coal freighter, the Nellie M, burst in on its crew as they watch television, shove them into rubber life rafts, set three bombs, and send the ship to the bottom in shallow water in a lake between Ulster's County Derry and the Irish Republic's County Donegal.
* Theatrically, 500 men stand beneath a flapping Union Jack on a windy County Antrim mountainside at night. A whistle blows. The men, in rows of 50, brandish pieces of paper said to be registration certificates for firearms. The Rev. Ian Paisley, Protestant leader, shouts that the guns will be used to stop Ulster being united with the Catholic south.
* IRA prisoners at the Maze jail in Ulster threaten a new hunger strike.
Hopes had been rising cautiously since British authorities and the 500 IRA prisoners at the jail reached an agreement in December. The British agreed that the terrorists could wear civilian (not prison) clothing and stay away from prison work. The men claimed this proved they were political, not criminals prisoners.
Since then, the prisoners have grown angry at what they see as a delay in granting these privileges.
Mrs. Thatcher and Mr. Haughey held another meeting in late December, which gave rise to Protestant fears that they were planning to impose a united Ireland. And the IRA has stepped up its own level of violence and killings.
In January, the IRA shot a leading Protestant and former speaker of the abolished Northern Ireland parliament, Sir Norman Stronge, and his son, claiming retaliation for the shooting of Catholic activist Bernadette Devlin McAliskey a week earlier.
Meanwhile, Mrs. Thatcher is under new pressure to talk publicly about "joint studies" going on with Dublin about the future. The problem is to handle the Protestant backlash in Ulster, since she has markedly failed to rule out a referendum there or an imposed un ion of north and south.