IN A FLURRY of recent articles speculating on the nature of a potential U.S. invasion of Iraq, reporters and commentators have raised a "nightmare" scenario: that a battle for Baghdad would turn into a second Mogadishu. With virtually no chance to survive--let alone win--a force-on-force conflict outside of Iraq's capital, Saddam would retreat to the close quarters of the streets of Baghdad, the thinking goes. There, the Iraqi army would exact a tremendous price in American blood. In effect, the fighting in Baghdad would be an epic version of the 1993 battle of Mogadishu, as chronicled in the book "Black Hawk Down" and dramatized in the recent movie.

But the only thing epic about this scenario is its distortion of recent history. Indeed, almost every aspect of a fight in Iraq--political, strategic, operational, and tactical--would be fundamentally different from that in Somalia.

The biggest and most obvious difference would be in the American government's will to win. In Somalia, the first Bush administration thought it was simply delivering food to starving people, and the Clinton administration was unwilling to back a broader agenda with a larger and adequately equipped force. In Iraq, by contrast, President George W. Bush has left no doubt that he means to remove Saddam Hussein and his henchmen from power. Accordingly, where the Clinton administration could walk away from Somalia without fundamental harm to its national security strategy, the Bush administration must succeed in Iraq. The Bush Doctrine--the essence of Bush's presidency--depends upon it. A half-hearted campaign is not in the cards. The fact is, while "will" is not the only ingredient required for success in war, it matters a great deal. And in a world with a single superpower, it is the essential variable.

Operationally, fighting in Baghdad would be part of a larger campaign to "take down" all of Iraq as rapidly as possible. Indeed, as the New York Times reported last week, attacks on Baghdad could well come in the initial phase of a larger Iraq campaign. And even if it didn't come first, any "siege of Baghdad" would follow quickly upon successes elsewhere across the country. Given the overwhelming advantage the Americans and their allies would hold outside the city, Iraqi forces (both elite and not) would realize this was the end of the line for Saddam and company. Whether the leaders of the Republican Guard would fight to the death at that point is unknowable, but it is likely the rank and file would not. Iraq's soldiers know that an American conquest of their capital will not result in the wholesale destruction of their homes and the slaughter of their families.

However Saddam came to power and ruled in his early days, he has remained in power by creating overwhelming fear among his subordinates. Once he loses the ability to sustain that fear, how can he maintain the discipline and loyalty of a sufficient number of troops to hold out in Baghdad?

No doubt some in Saddam's inner circle figure that, once captured, they will be held accountable for the crimes they have perpetrated against their countrymen. On the other hand, being captured, tried by an international tribunal, and sentenced to life in prison beats dying a violent death for the sake of a tyrannical thug. No doubt many of Saddam's cronies will prefer to rip off their uniforms and try to disappear into the crowds of Baghdad or into the countryside en route to escaping from the country. This was the choice made by many in Manuel Noriega's Panama Defense Force in 1989 (when, by the way, there was significant urban combat). Once Noriega's officers and soldiers reckoned that he would no longer be ruling Panama--and that the Americans would--their perception of their own interests was reversed. Generals in Iraq who have understood President Bush's rhetoric over the past year may already have made this calculation.

Finally, the tactical situation facing U.S. troops in Baghdad would be different from that in Mogadishu. Their purpose would be to capture the city and destroy the last remnants of organized resistance--a conventional, if difficult, operation--not to arrest an individual using only elite forces in a "strike and grab" operation.

Where Somali warlord Mohamed Farah Aideed's clansmen had spies inside the U.N. headquarters and were able to observe American operations close at hand over a period of months, including several operations targeted at Aideed and his command structure, an Iraqi force in Baghdad would have no such experience. They would surely "prepare the battlefield," as soldiers say--boobytrapping buildings, for example--but their ability to predict precise U.S. tactics would not be enhanced by the kind of preparation the Somalis had.