War is very rarely a scheduled event. It comes by stealth, often in the shroud of night. It begins, as American involvement in World War II did, by sneak attack, or sometimes, as it did in World War I, when the very physics of geopolitics whirls out of control. The world seldom has a chance to get ready for war.

But what we are witnessing now — the slow, public mobilization to war, with many elements of calculation but no element of surprise — represents an extraordinary moment in history. And it permits us to say in advance the unmistakable but unavoidable truth that almost always is said only in retrospect: Much of the diplomatic, political, economic and cultural character of the next decade may be determined by what happens in the next month.

Indeed, the world will be reshaped by whether, as expected, President Bush sends American forces into battle in Iraq and how, if he does, the war progresses, how long it lasts, how wide it gets, how broad its implications are, how sweeping the unintended consequences are. In World War I, the unintended result was the destruction of the Ottoman, Austro-Hungarian and Russian empires. In World War II, the unexpected consequence was the virtual end of Great Britain as an empire and major power. Indeed, few episodes in modern times have the potential of transforming so much in so short a period:

The shape of the Middle East. The aim of the Bush administration is to topple Saddam Hussein, install a new government dedicated to democratic principles, reverse decades of deprivation, repair the damage of the invasion itself, and create a model for a new state, intended to be a model for its neighbors. In the best of all worlds, that vision may prevail. But any invasion of Iraq inevitably will also change the political calculus throughout the region, perhaps endangering other, reasonably stable Arab nations like Saudi Arabia and Egypt and perhaps threatening Israel. Whatever happens, the Middle East will be substantially altered by May.

The future of the United Nations. Countries on both sides of the great divide over Iraq recognize the next few days as the most critical test of international governance since the North Korean invasion of South Korea in June 1950, which tested United Nations resolve against aggression, or perhaps even the Italian invasion of Abyssinia in October 1935, which is remembered as a symbol of the fecklessness of the League of Nations.

The presidency of George W. Bush. No president is left untouched by war, and some, like Abraham Lincoln and Lyndon Johnson, are nearly broken by it. Bush became a war president in a metaphorical sense on the morning of Sept. 11, 2001. Next week he could be a war president in earnest. At last weekend’s Gridiron Club dinner, traditionally an evening of lore and laughs, Bush — his face grave, his determination palpable — rose and gave perhaps the briefest presidential speech in the 118 years of the club, a solemn toast to America’s fighting men and women gathering near the Persian Gulf. Then he sat down. The first President Bush is remembered for the combat in the Gulf, to be sure, but was judged by the economy; for the son, the reverse could be true.

The future of warfare. Gulf War II will be the showcase of a new generation of arms that make the weaponry employed in Gulf War I seem almost primitive in comparison. But American military personnel may be exposed to dangers that make the threats from the previous engagement with Iraq seem tame. If Saddam Hussein’s forces employ chemical, biological or nuclear weapons, a forbidden threshold will be passed, making the practice of war even more terrible than it is now.

The course of the economy. The terrible costs accumulate, as Winston Churchill might be prompted to say. The price of transporting American troops to the Gulf region could be almost $25 billion. The Defense Department estimates the war may cost $60 billion. The price of a gallon of gasoline, according to the American Automobile Assn. daily tracking survey, is $1.69, and it may be heading toward $2. No one knows the economic consequences of the peace. Here’s the context: The Congressional Budget Office now estimates the fiscal 2004 budget deficit will reach $338 billion. It will not get smaller as a result of the war,

The American role in the world. At no time in modern history have America’s relations with so many European nations been so troubled. Not since Vietnam has America’s determination to make its own course in world affairs sent so many protesters to the streets — and to microphones in the Security Council. Much of that can be dismissed as the price of power in a world that no longer sets captive nations against free ones. But the importance of this passage should not be underestimated. The ability of the United States to mobilize and motivate its traditional allies has been undermined, and for the first time in more than a half-century, NATO can no longer be counted on as the anchor of U.S. diplomatic and defense thinking.

And so the stakes in the next week, and in the months that follow, are bigger than the survival of Saddam Hussein. He may turn out to be a bit player in history, but the drama prompted by his cameo role on the world stage will endure beyond his own life. It may well be the story of our times.