It would start with a fierce air bombardment. Next, special forces could fan out to create "no-movement" zones and then search for biological and chemical weapons. Predator remote-controlled planes would patrol for Scuds on the ground.

In the end, however, it would take a much more massive military commitment than in Afghanistan if the United States were to attack Iraq.

In all, analysts say, 100,000 or more American troops might be needed against Saddam Hussein, who could shield his elite Republican Guard troops by placing them among Baghdad's civilians — and who might retaliate with chemical attacks.

"It is a major, major decision," Sen. John Warner warned the Bush administration last week. If the government is contemplating full-scale military action against Iraq, "We've got to prepare the American people for what the consequences would be," said Warner, R-Va.

U.S. officials say they have not decided whether to attack Iraq. The administration accuses Saddam of developing weapons of mass destruction and sponsoring terrorists, and says it is considering options from diplomatic pressure to covert action to military strikes.

If Bush did decide on military action, he would have options ranging from isolated airstrikes to support for Iraqi rebels to a full-scale assault aimed at overthrowing Saddam.

"Anything short of a ground invasion would run a high risk of failure," said Philip Gordon of the Brookings Institution, who echoes many analysts in saying that if military action is taken, it must be decisive.

An attack generally would feature more special forces and more precision bombs than were used in the 1991 Gulf War.

Most analysts believe an attack would not come before the fall because the administration would give Saddam a chance to readmit U.N. weapons inspectors first. The United States also would need several months to build up troops in the region, as well as restock precision-guided munitions depleted during the Afghan fighting.

Iraq is much more robust militarily than the Taliban who ruled Afghanistan, although Iraq is weaker than before the 1991 war. It now has an estimated 2,000 tanks, several hundred aircraft, about 350,000 to 400,000 troops and a fairly sophisticated air defense system.

If an air campaign were to begin, Saddam might try to launch Scud missiles, perhaps with chemical or biological weapons on them, against Israel or U.S. troops, said retired Rear Adm. Stephen Baker of the Center for Defense Information in Washington.

The United States could use unmanned, armed Predator aircraft to try to search for and destroy Scud launchers and the missiles themselves before they are fired.

"Handling this threat will be one of the hardest, most challenging missions in Iraq," Baker said.

The United States also might try to insert special forces teams to create areas under U.S. control where the Iraqi army could not operate and where Americans could search for elusive biological, chemical and nuclear weapons sites.

Several carrier battle groups probably would be in the area — one or two in the Red Sea and two or three in the Persian Gulf — to launch airstrikes or perhaps serve as a base to insert special forces, Baker said.

The Air Force would want to operate bombers from bases in Saudi Arabia, Kuwait, Turkey and the British-controlled island of Diego Garcia — depending on who allowed that. Ground operations might be staged mostly from Kuwait.

Only cooperation from Kuwait is necessary to begin an invasion, but cooperation from Saudi Arabia would help immensely, said Kenneth Pollack, director of national security affairs for the Council on Foreign Relations.

U.S. officials say they are taking steps, including moving equipment to a base in Qatar, to ensure they could spearhead a war in the Gulf, even if Saudi Arabia refused to allow U.S. operations on its soil.

U.S. forces have been increased in recent months in Kuwait — from 5,500 to about 10,500 — but only to warn Iraq not to make threats against its neighbors, defense officials say.

The number of U.S. military personnel in the Gulf region and Central Asia — from Saudi Arabia to Pakistan — has increased from fewer than 25,000 to nearly 80,000, since the Sept. 11 terrorist attacks.

The U.S. military also might send special forces teams to work with Kurds or with Iraqi dissident groups in the north, where Saddam's army cannot operate because of a no-fly zone.

One hope is that once U.S. military action began, those groups would rebel. If Saddam seemed in jeopardy, regular army soldiers and officers might rebel. It is unclear how loyal the Republican Guard would prove.

Another problem would loom if Saddam tried to place the Republican Guard in Baghdad. The United States would have to decide whether to attack at the risk of killing Iraqi civilians.

And, there is always the wild card that Saddam might launch other attacks with weapons of mass destruction if he felt personally threatened.

In the end, many analysts believe America would succeed if it launched a full-scale invasion, although it probably would mean casualties.

But then, the tough job of stabilizing Iraq would begin — an effort that could mean placing tens of thousands of U.S. military troops in Iraq for years to come as America and others scramble to find a stable leader.

"Removing Saddam will be opening a Pandora's box, and there might not be any easy way to close it back up," Gordon said.