Some estimate that it would take thousands, if not tens of thousands, of troops to patrol Iraq, especially Baghdad, where the prospect of revenge killings, ethnic rivalry, terrorism and a humanitarian crisis could dwarf the urban perils faced by U.S. troops in Somalia in 1993.
the Army based on 16 U.S. military occupations in the 20th century - dating to the Philippines in 1902 - estimates that about 100,000 occupation troops would be required to patrol a post-Hussein Iraq.
Moreover, a former strategist for the Joint Chiefs of Staff, retired Army Col. Scott Feil, predicts that 75,000 U.S. troops would be needed for the first year, with an undetermined number after that.
A force of that size would carry a high price tag. Feil, director of strategy for the Joint Chiefs in 1999-2000, placed it at $16 billion for the first year.
Still, some say the number of troops needed for an occupation - and the associated costs - can only be determined after the fight. Anthony H. Cordesman, an analyst with the Center for Strategic and International Studies, said that suggesting a number beforehand is akin to "predicting the outcome of a slot machine."
"Certainly we should have a significant presence," he said. "We're not going to do that, it's clear, with 500 men."
The prospect of a large occupation force is troubling some members of Congress as they take up a resolution that could grant President Bush sweeping authority to remove Hussein from power and eliminate his weapons of mass destruction.
"How many troops will be needed for peacekeeping? Ten thousand? A hundred thousand or more? That's my main concern," Rep. Ike Skelton of Missouri, the ranking Democrat on the Armed Services Committee, said in an interview. "I don't think Iraq will be militarily that difficult. What you do after [the invasion] could be a mess."
In addition, current and former military leaders fear that an extensive occupation could further stretch the active and reserve components of the U.S. military, particularly the Army, which is already engaged in operations from the Balkans to the Sinai desert to Afghanistan.
Retired Marine Gen. Anthony C. Zinni, who stepped down in 1999 as commander of U.S. forces in the Middle East and Central Asia, said that besides stretching the military too thin, "I worry about the commitment and cost of the aftermath."
Already, senior military officers with the Special Operations forces - including the Green Berets, who were key to the defeat of the Taliban in Afghanistan - have told Pentagon leaders that it would be difficult to undertake another major military operation without cutting back elsewhere, such as anti-drug operations in South America or training missions in Africa, said one Pentagon official. Civil affairs units from such forces are key to helping new governments get under way, assisting in everything from personal security to rebuilding schools.
Said one Army officer: "The increased focus on Iraq along with our existing commitments has many of us scratching our heads as to how we can do all of the missions assigned, especially given the stress reported by the National Guard and Reserve and increased homeland defense commitments."
The Army has embarked on a study, due in December, that will determine whether its 480,000-soldier force is adequate to carry out current worldwide obligations, an Army official said. Some officers have been pressing for an increase of 40,000 to 50,000 soldiers.
A senior Pentagon official brushed aside the concerns of the Army and others, noting that with a force of nearly a half-million men on active duty and an Army National Guard and Reserve force of more than 700,000, there should be plenty of soldiers for an invasion of Iraq and an occupation force. "The fact is we're going to be stretched, and we're going to have to sacrifice," he said.
Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, told Congress last week: "We do have sufficient capability to conduct effective operations against Iraq while maintaining other aspects of the war on terrorism, protecting the U.S. homeland and keeping our commitments in other regions of the world."
Military officers and analysts worry that the Bush administration has not made the same progress in fashioning a post-war strategy as it has in drawing up war plans. Administration officials continue to meet with the fractious Iraqi opposition groups but so far have not come up with a framework for a democratic Iraq.
A senior administration official, who requested anonymity, said that the Iraqi opposition groups "have a substantial way to go to be a catalyst for a new Iraqi regime."
Cordesman, the CSIS analyst, said there has been a "deafening silence" from the administration about how Iraq will be run after Hussein. Afghanistan has shown the world there can be no "instant democracy," he said.
Phebe Marr, an Iraq specialist for four decades who retired in 1997 from the National Defense University, told the Senate Foreign Relations Committee last month that the United States must be willing to make "a long-term military and political commitment" to Iraq should it overthrow Hussein.
There is some speculation that the Kurdish groups would seize the oil-rich region centered on the northern Iraqi city of Kirkuk, now controlled by Hussein but seen as part of the Kurdish territory. Such a move might cause Turkish troops to intervene to protect the Turkmen minority in that city - but mostly to prevent the oil from falling into Kurdish hands. Turkey also fears that the ethnic Kurds within its borders might try to join with those living in Iraq to form a separate country.
Iran might also be a factor. Some analysts say that one of the Iraqi Shia groups based in Tehran and opposed to Hussein could send in forces to capture areas of the south, where their religious brethren are located.
Marr and others say an international force would be preferable to a large, nearly exclusive U.S. presence. Before long, U.S. troops would be seen as an occupying force and incur the wrath of the intensely nationalistic Iraqis, Marr said.
It is that situation that most troubles military officers: bogged down and surrounded by a hostile populace, troops separating warring factions in places such as Baghdad, a sprawling city of nearly 5 million, while also handling humanitarian relief. For centuries, military leaders have feared fighting or patrolling cities, where buildings, houses and alleyways can serve as easily defensible roosts for enemies. And in the midst of fighting, civilian casualties can quickly mount.
Baghdad "would be like Jenin," said retired Army Gen. Wesley Clark, a former commander of U.S. and NATO forces in Europe, referring to the West Bank refugee camp that was the scene of house-to-house fighting between Palestinians and Israeli soldiers this year.