THE HOPE of genuine civic peace in Northern Ireland seems stronger today than for many St. Patrick's Day past. Britain is now treating the intermittent guerrilla warfare there as a matter of international politics. For many years the British government had insisted on considering it purely a domestic affair. But last December, in a notable act of statesmanship, Prime Minister Thatcher of Britain went to Dublin for meetings that acknowledged the Irish Republic's inevitable role in the outcome. Perhaps there was also, by implication, a degree of recognition that a great many Americans also have more than a passing interest in Irish affairs. The cooperation between Dublin and London gives a new substance to the promise of an end to the tit-for-tat campaigns of assassination and bombing between the IRA and its Protestant counterpart that have now been going on for 10 years.

Mrs. Thatcher, in Belfast last week, asserted again her determination to keep working "between nation and nation, between community and community." The Republic's Prime Minister Haughey, a few days later, spoke of a spreading belief that this cooperation has become "the most hopeful development . . . in a situation in which it would have been all too easy to give way to despairing inactivity."

A great many Americans of Irish descent, particularly in the earlier stages of the fighting in Northern Ireland, were giving money to the IRA. The IRA was supposedly using it to fight the British Army but, in fact, the bombs mostly killed Irish civilians. As the bloodshed continued, on St. Patrick's Day 1977, four very prominent Americans with Irish names courageously urged an end to the violence, and an end to the flow of dollars that supported it. Today the four -- Speaker O'Neill, Senators Kennedy and Moynihan and Governor Carey of New York -- repeat their call, and this time they are joined by 18 more senators and congressmen, as well as the govornors of New Jersey and Rhode Island. They announce the founding of a new organization, the Friends of Ireland, to support a peaceful settlement.

The Republic of Ireland yearns for the unification of the island, north and south. The British government properly insists that there can be no change in the status of Northern Ireland without the assent of a majority of the people who live there, and full protection of the rights of the Protestant community. The American group, the Friends of Ireland, accepts both the goal and the condition. "On this St. Patrick's Day, we ask all Americans to join our cause, to reject the bomb and the bullet, the fear and the terrorism," the Friends said. "We look to a future St. Patrick's Day, one that we can foresee, when true peace shall finally come . . ."