Protestant pro-British militants in Northern Ireland laid down their arms in what may be the final act in setting up a durable peace in the region. The paramilitaries announced that they will "universally cease all operational hostilities," effective midnight tonight. They also went further than the I.R.A., which first declared a cease-fire on Aug. 31; the Protestant forces apologized for the hundreds of deaths they caused. The Irish government and the I.R.A. quickly embraced the overture.