CHRISTMAS EVE seems made for memory. I remember being wedged among my brothers, all of us between our parents, in the crowded balcony of St. Mary's Church for midnight Mass. The aroma of incense, the hissing of a nearby radiator, the unpadded kneeler hard against my knees, my mother's rosary beads swaying below her tan gloves.
The best part of Christmas Eve was the cold, clean air coming out of church, the ride home in the car, the exotic feeling of being out so late. The worst part - how impossible it was to keep my eyes from fluttering shut even as my brothers debated whether Santa Claus would come to a house whose occupants were all away at Mass.
But as the music of bells and carols yield to the drums of a mounting military cadence, America about to go to war, another Christmas memory intrudes. This year marks the 30th anniversary of the Christmas bombing of North Vietnam. For people of a certain age, the thought of that unprecedented air assault, lasting from Dec. 18- 30, intermittently disturbs the tranquility of the otherwise holy season. How staggered we were at reports of the bombs falling day and night on cities across North Vietnam. Hanoi and Haiphong were especially hard hit.
American pilots flew nearly 4,000 sorties, including more than 700 by high-flying B-52s. Those ''area bombers,'' incapable of precision, had never been used against cities before. That they were used now was a sure sign that this was terror bombing pure and simple.
Washington said its penultimate air campaign was necessary because Hanoi had balked at the peace talks, but most of the balking was obviously coming from Washington's Saigon ally. Everyone could see that the bombing was a final venting of frustration and rage by a superpower faced with ignominious defeat.
The reason to remember the Christmas bombing of 1972 is not to feel morally superior to those responsible for it. Rather, it is to understand something basic to the experience of war. Here is the most important truth of this memory: Those who ordered and carried out the brutal attacks against population centers at the end of the Vietnam War would never have done so at the beginning. What Nixon commanded in 1972 he would have condemned in 1969.
The war transformed America's moral sensibility; the war deadened it. It had happened before. In 1939, the American president pleaded with the nations that had gone to war in Europe; ''Under no circumstance,'' FDR said, ''undertake the bombardment from the air of civilian populations or of unfortified cities.'' By the end of that war, the US Air Force had defined itself as an instrument of urban destruction, replacing cities with piles of rubble (81 of Japan's largest 120 cities were obliterated from the air, even before Hiroshima). What Washington abhorred at the beginning was taken for granted by the end.
The dynamic of war transcends the ability of warriors to resist it. In war, choices routinely lead to unanticipated consequences, which present wholly unimagined new choices, which involve further consequences, leading finally to choices to which warriors would never have given assent at the start. Because of this human inability to foresee or control descent into savagery once killing begins, the only way to keep war ''humane'' is not to embark on it in the first place.
But sometimes the coming moral horror presents itself in prospect with clarity and force. When President Bush announces, as he did two weeks ago, an American readiness to use nuclear weapons in retaliation against any use by Saddam Hussein of chemical or biological weapons against US forces, he is, in effect, ceding to Saddam the primacy of moral judgment. He is saying that, under certain foreseeable circumstances, which may or may not be likely, the United States will join Iraq in crossing the threshold into the ethical abyss of mass destruction.
By raising the specter of nuclear use, President Bush is already defining the war he is about to initiate as a war without moral limit. Having imagined choices and consequences to that extent, alas, he does not seem to have considered what will follow from an American return to the exercise of power by nuclear terror: a savage century. To his credit, though, the president has given the world and his nation a fair description of what he imagines he might do. A fair warning, and not only to Hussein.
Have we heard it? On this Christmas Eve, which is nearly the eve of an aggressive American war, the nation goes down on its knees to pray for peace. We worship memories of our own virtue. What lies we tell ourselves! Santa Claus is coming tonight. We are the forces of good arrayed against evil. Yes, and Nixon's Christmas bombing brought us peace with honor.