Precisely what led the Irish Republican Army to destroy some of its weapons this week may never be known. Perhaps the decades-long policy against disarmament was reversed by the realization that the soil of Northern Ireland has soaked up too much blood, perhaps it was the current worldwide revulsion against terrorism. Regardless of the stimulus, it is a most welcome response.

It also is an opportunity that must not be wasted. The weapons “put beyond use” – firearms, ammunition and explosives – are but a small part of the IRA arsenal. Further disarmament depends upon matching concessions by the British government, a hint of which came with the immediate announcement by London that several military posts in Northern Ireland will be demolished. Police reform, eliminating the “religious profiling” of Catholics, must come next.

The small step taken is a major advance for Gerry Adams, president of the IRA’s political wing, Sinn Fein. Mr. Adams, a former IRA member, has long advocated transforming the struggle for a unified Ireland from warfare to politics. The stock of David Trimble, leader of the main pro-British Protestant party, also rose. Mr. Trimble resigned his post as head of Northern Ireland’s executive branch in July in protest of the IRA’s intransigence on disarmament, the Protestant parties withdrew from the joint government last week for the same reason. Within hours of the weapons destruction, Mr. Trimble announced be would bring his Ulster Unionist Party back into the government and would work with Mr. Adams to revive the 1998 Good Friday power-sharing agreement between Catholics and Protestants.

Despite more than 3,000 dead, a military solution to this decades-old strife still has its advocates, presenting enormous diplomatic challenges to both leaders. Mr. Adams must contend with the so-called Real IRA, a dissident group that is opposed to power sharing and that has embraced violence as the means to drive the British out of Northern Ireland. Similarly, Mr. Trimble must rein in several paramilitary Protestant groups.

As the majority for peace grows, the minority for war becomes increasingly in

discriminate and savage; this heartening progress for peace almost certainly will be answered outrageous acts committed by those who derive their power from bloodshed. Mr. Adams and Mr. Trimble must reach across the religious boundaries as they simultaneously shore up support within their constituencies to keep these well-armed thugs from squandering what has been bought at such high cost.