BERTIE AHERN, Ireland's prime minister, caught the moment when he said Northern Ireland is on the threshold of securing a lasting peace. The fresh commitments extracted by the inventive and indefatigable American mediator, George Mitchell, still need to be delivered on. The mood is of hope but of caution, too.

The deal waiting to be finally struck would have the leading mostly Protestant party of David Trimble set up a first power-sharing executive body including the leading mostly Catholic party of Gerry Adams. Mr. Trimble took a brave leap by dropping his insistence that IRA disarmament start first. But the IRA, the Irish nationalist Sinn Fein party's military wing, did promise to send a representative to an international commission established for the purpose of disarming Ulster.

Whether Mr. Adams can induce his erstwhile comrades in the IRA to abandon the gun and allow a political process to unfold -- a course it has heretofore regarded as surrender -- will become known as events evolve. The more dramatic showdown, however, may well come from Mr. Trimble. He faces heavy opposition to the Mitchell compromise package from elements in his Unionist party reluctant to let go of their traditional privilege. The party's decision-making council gathers on Nov. 27.

One hesitates to say this is Northern Ireland's "last chance." But most people would probably concede that it is simply not possible to imagine how the disruption of this accord could bring profit to anyone except the men of violence on both sides. Failure would deny Ulster's Protestants and Catholics alike the chance they still have, despite everything, for a decent future.