WASHINGTON -- Unless Iraq's military capitulates quickly, the most difficult phase of a war to overthrow President Saddam Hussein will likely be the battle for Baghdad. American military triumphs since 1990 have taken place in the open desert of Arabia, the airspace over the Balkans and the barren plains of Afghanistan. Fighting in cities is a different matter; exercises and simulations show it remains an enormous challenge even for today's U.S. armed forces.

Would a battle for Baghdad be, as some have suggested, a "Mesophotamian" Stalingrad, similar to the brutal German siege of that Soviet city in World War II? Or would it be a rout in which the Iraqi population comes to America's aid and quickly deposes Hussein?

Of course, no one can know in advance. But a war that many forget may provide the best clues. In December 1989, just over 20,000 American troops invaded Panama to depose that country's strongman president, Gen. Manuel Noriega. The war, centered on Panama City, was over in a week; intense fighting lasted just a few days. In addition to the 10,000 American troops stationed in Panama, light and mechanized infantry units deployed from the United States, and -- as likely would be the case in Iraq -- special-operations units played a significant role.