The administration is turning to that approach after concluding that a coup in Iraq would be unlikely to succeed and that a proxy battle using local forces there would be insufficient to bring a change in power.
But senior officials now acknowledge that any offensive would probably be delayed until early next year, allowing time to create the right military, economic and diplomatic conditions. These include avoiding summer combat in bulky chemical suits, preparing for a global oil price shock, and waiting until there is progress toward ending the Israeli-Palestinian conflict.
Until recently, the administration had contemplated a possible confrontation with Mr. Hussein this fall, after building a case at the United Nations that the Iraqi leader is unwilling to allow the kind of highly intrusive inspections needed to prove that he has no weapons of mass destruction.
Now that schedule seems less realistic. Conflict in the Middle East has widened a rift within the administration over whether military action can be undertaken without inflaming Arab states and prompting anti-American violence throughout the region.
In his public speeches, President Bush still sounds as intent as ever about ousting Mr. Hussein, making it clear that he will not let the Middle East crisis obscure his goal. But he has not issued any order for the Pentagon to mobilize its forces, and today there is no official "war plan."
Instead, policy makers and operational commanders are trying to sketch out the broad outlines of the confrontation they expect.
Among the many questions they must address is where to base air and ground forces in the region.
Even before Mr. Bush's tense meeting with Crown Prince Abdullah of Saudi Arabia on Thursday, the Pentagon was working on the assumption that it might have to carry out any military action without the use of bases in the kingdom.
The planning now anticipates the possible extensive use of bases for American forces in Turkey and Kuwait, with Qatar as the replacement for the sophisticated air operations center in Saudi Arabia, and with Oman and Bahrain playing important roles.
As to any war plan itself, the military expects to be asked for a more traditional approach than the unconventional campaign in Afghanistan. Such an approach would resemble the Persian Gulf war in style if not in size and would be fought with even more modern weapons and more dynamic tactics.
"The president has not made any decisions," a senior Defense Department official said. "But any efforts against Iraq will not look like what we did in Afghanistan."
Vice President Dick Cheney, Defense Secretary Donald H. Rumsfeld and their senior aides contend that Arab leaders would publicly protest but secretly celebrate Mr. Hussein's downfall — as long as the operation were decisive — and that ousting him would actually ease the job of calming violence between Israel and the Palestinians. They believe that warnings of uprisings among Arab populations are overblown and compare them to similar warnings before the gulf war, which proved unfounded.
"It has been the consistent drumbeat from our friends in the region that if we are serious, they will be with us," said an administration official in this camp.
But others at the State Department and the White House argue that efforts to topple Mr. Hussein would be viewed by Arabs as a confrontation with Islam, destabilizing the region and complicating the broader campaign against Osama bin Laden and his network, Al Qaeda.
The reaction in Saudi Arabia is already critical. The United States would need permission to use Saudi airspace adjacent to Iraq, if not Saudi air bases, officials said, but it is unclear whether Mr. Bush took up that subject with Crown Prince Abdullah when the topic of Iraq came up. Mr. Rumsfeld, who met with the Saudi leader a day ahead of Mr. Bush, said access to bases "was not a topic at all" of his discussions.
Turkish officials, for their part, said that no negotiations on basing American troops for a new campaign against Iraq had yet taken place; American officials confirmed that, calling such talks premature.
Kuwait's position, too, is uncertain. At an Arab League summit meeting in March, Iraq agreed to recognize Kuwait and pledged not to invade again in exchange for a declaration that an attack on Iraq would be considered an attack against all Arab states. But American officials said they could rely on Kuwait, whose very survival is owed to American military power after Iraq invaded the country in 1990.
Senior administration, Pentagon and military officials say that consensus has emerged that there is little chance for a military coup to unseat Mr. Hussein from within, even with the United States exerting economic and military pressure and providing covert assistance.
"There have been at least six coup attempts in the 1990's, and they consistently fail," an administration official said. In each instance, this official said, dissident Iraqi military officers "sent signals to us, `We're ready for a coup,' and the next thing you know these guys are murdered or it fails or people have cold feet at the end and leave the country."
"It's a horrific police state," the official said. "Nobody trusts anyone, so how can you pull off a coup?"
Similarly, officials say they do not believe that even an expanded version of the strategy used to oust the Taliban from Afghanistan would work. In that model, precision airstrikes combined with indigenous armed opposition under the leadership of American Special Operations forces and C.I.A. officers did the job.
The parallel strategy in Iraq would involve the Kurds in the north and the Shiites in the south. But Mr. Hussein's military, while only one-third its strength from before the gulf war, is strong enough to defeat any confrontation by proxy, officials said.
Officials said the nascent plans for a heavy air campaign and land assault already included rough numbers of troops, ranging from a minimum of about 70,000 to 100,000 — one Army corps or a reinforced corps — to a top of 250,000 troops, which still would be only half the number used in the gulf war. Other than troops from Britain, no significant contribution of allied forces is anticipated.
The military requirements for changing the government in Baghdad would be vastly different than the gulf war mission, which was to drive an entrenched enemy from a large occupied area, senior military officers said.
"We would not need to hold territory and protect our flanks to the same extent," one officer said. "You would see a higher level of maneuver and airborne assault, dropping in vertically and enveloping targets — less slogging mile by mile through the desert."
Even so, officers said, moving tens of thousands of troops to a region with access more limited than in the gulf war could be a logistical challenge. The modern American military has never fought the kind of dangerous and complicated urban battles that might be needed to oust the Hussein government.
Dealing with Mr. Hussein's suspected chemical and biological weapons would require pre-emptive strikes by precision weapons, as well as an element of heavy deterrence.
"One of the things we would want to do is say that any Iraqi officer or soldier who throws chemical or biological weapons at us will be held personally responsible," said Eliot A. Cohen, a professor at Johns Hopkins University who directed the Air Force's definitive study of the Persian Gulf war. "You say, `You guys operating the missile batteries: we will find you, and you will pay.' Saddam's people have no desire to go down in a blaze of glory with him."
While the Pentagon has focused on how to remove Mr. Hussein, the White House is also mindful of the effects of a war on oil supplies — either because the fighting itself would disrupt the flow of oil, or because Saudi Arabia and other Arab producers would feel obliged because of political pressure at home to cut exports to the United States.
R. Glenn Hubbard, chairman of the White House's Council of Economic Advisers, said the administration had examined the possible effects of a spike in oil prices caused by spreading unrest in the Middle East or an invasion of Iraq.
He said a surge in oil prices would probably not by itself have a large effect on the American economy. But he said it was more difficult to assess the possible effects on consumer and business confidence. One of the lessons of the gulf war, he said, was that consumer confidence recovered once the United States made clear that it intended to expel Iraqi forces from Kuwait and guarantee the security of the Saudi oilfields.
In November, Mr. Bush ordered that the government's Strategic Petroleum Reserve be filled to capacity. A review of the reserve's delivery schedule shows that many of the largest monthly deliveries are between September and January, another reason to put off any offensive against Iraq to early next year.
"We want to be in a position to go into the markets if speculators begin bidding up the price of oil, and settle them down fast," one official said.