As President Bush and his aides dig in for a longer war than first hoped for, they face a sobering prospect: Longer and tougher combat will create a ripple effect of problems stretching from the battlefield to the rest of the world -- including the home front.
A worst-case scenario of brutal, drawn-out urban warfare in Baghdad would not only cost the lives of many more U.S. troops and Iraqi civilians, it would sharpen anti-American passions in the Islamic world and could even slow an economic recovery in the United States.
"In chaos theory, it's said that a single beat of a butterfly's wing can cause a tornado somewhere else," said John Lewis Gaddis, a historian at Yale University. "We're in one of these butterfly situations now.... The longer the war goes on, the more difficulties we're going to have elsewhere in the world."
It's still possible that the war could end in a matter of weeks, without house-to-house fighting in the Iraqi capital.
"We will know a whole lot more when the battle of Baghdad begins," said Sen. John McCain (R-Ariz.). "That battle will have a big effect on the length of it. But I still believe it will be a short war -- a month or two months."
But the stiff resistance shown by Iraqi forces in the last week has forced administration officials to consider the prospect of a longer, costlier war, and the spinoff effects it could have.
"So much depends on what we have to end up doing about Baghdad," said an advisor to the Bush administration. "There are no palatable options in urban warfare."
Administration officials acknowledge that public expectations of a quick and easy war -- fed, in their view, by overenthusiastic media reports -- could create real political problems at home. Even a few Republican members of Congress privately expressed unease in briefings about the war last week: "Is this going to get worse?" one asked, according to an aide.
That's one reason Bush and Defense Secretary Donald H. Rumsfeld launched a major effort last week to manage expectations. "We have seen mood swings in the media from highs to lows to highs and back again, sometimes in a single 24-hour period," Rumsfeld complained. "Fortunately, my sense is that the American people have a very good center of gravity."
Their vigorous defense of the war's progress reflected another factor in administration thinking: The long-term results of the war -- not only how soon victory might come, but what kind of victory it might be -- depends on the clash of arms and on how it is perceived around the world.
"The next several weeks will determine" what kind of victory the United States can claim, Gaddis said. "They will not necessarily produce a final resolution to the war, but they will tell us what kind of war we're in."
An early victory could have the effect of legitimizing Bush's decision to go to war and confirming America's status as an unchallengeable superpower. And if, on the way, U.S. troops find Iraqi chemical or biological weapons, "that could turn the whole psychology around, all over the world," Gaddis said.
But a long and costly war could send the opposite message: However intimidating U.S. military power appears, it can still be stymied -- at least temporarily -- by a determined guerrilla force.
A long war would mean more civilian casualties, more anger in the Arab world and a more difficult postwar challenge in rebuilding Iraq. It would mean more cost to Americans in both blood and treasure, dampen the chances for a domestic economic recovery, and potentially weaken Bush's chances of reelection. And it would provide more opportunities for crises to occur elsewhere -- in North Korea, Pakistan or Jordan.
"This is a very tricky period; relatively minor events can have big consequences," Gaddis said. "We've gone beyond strategy now. What happens on the ground is what matters."
In Iraq itself, some administration officials acknowledge they were surprised by the persistence of forces fighting for Saddam Hussein's regime.
"In a region that didn't want us to go to war in the first place, there is developing some admiration for brave little Iraq," said a former senior official and Republican who asked not to be named. "I'm not sure it's going to make Saddam a folk hero. But the longer it goes, the more people that get killed, the more we're going to look like a bully.... And that will have an impact on the postwar world."
In the region around Iraq, a longer war will make it more difficult for Arab countries such as Saudi Arabia and Jordan that are quietly supporting the U.S. war effort against the grain of their own public opinion.
"It's going to have an impact on other regimes and their willingness to cooperate with us," said Robert Oakley, a former U.S. ambassador to Pakistan. "It's not likely to topple them, although Jordan is worth worrying about.
"The CIA already expects to get less cooperation" from Arab intelligence services, he added -- and that "will make counter-terrorism more difficult."
The nature of the war will also affect how difficult and how long the U.S.-run postwar occupation of Iraq will be.
"The longer the war, the longer the occupation is likely to be," said Rep. John M. Spratt Jr. (D-S.C.), a senior member of the House Armed Services Committee. He said a longer war would produce more damage to clean up and "a more embittered population in Iraq."
In clan-based Iraqi society, another former diplomat warned, "if you kill 500 militiamen, you make 4,000 enemies. You aren't going to get much of a welcome from people whose husbands, sons and brothers you've just killed."
Public opinion in Europe, already largely opposed to the war, will probably consider its views confirmed if civilian casualties mount -- and that could pose problems for allied leaders such as Britain's Tony Blair and Spain's Jose Maria Aznar, who have supported Bush despite public pressures.
In the United States, pollsters say, public support for the war is holding steady at more than 70%, even though an increasing number of Americans say they expect more U.S. military casualties.
Public support appears unlikely to flag significantly as long as the war lasts less than six months, and as long as it appears on course toward victory, pollsters say.
But that doesn't mean support for the war -- or for Bush -- is unconditional.
"I think the American people are going to be there for the long haul," said Michael K. Deaver, a former advisor to President Reagan. "But if we sustain massive casualties ... and if it looks as if we put troops in harm's way because somebody made mistakes, then all bets are off."
Two other factors will affect U.S. public opinion -- and Bush's political future: the success of the postwar occupation, and the effect of the war and its aftermath on the domestic economy.
"The longer the war, the more willing people will be to criticize Bush and his policies," said Mickey Kantor, a former advisor to President Clinton. "This is not Vietnam, and it's not going to be Vietnam. But if it starts to feel like some kind of quagmire, people will be willing to talk about it. And if it adversely affects the economy ... it will make Bush more vulnerable to criticism on that issue."
So far, the war's economic effect has been only short-term: a wild swing of expectations and stock market prices, from pessimism to optimism and back again. But the longer the war, the more persistent the uncertainty that many economists believe is delaying many big business investments -- and holding up a broad economic recovery.
"Expectations are probably swinging too widely," said Richard D. Rippe, chief economist at Prudential Securities. "But a longer war would have some foreseeable impacts. The first one would be its impacts on the markets, particularly the oil markets. The stock market would be under more pressure.... And a prolonged period of uncertainty would make consumers hesitant to spend."
The direct costs of the war, while stiff, are unlikely to change the economy's basic course, economists say. Spratt said the Congressional Budget Office has estimated that waging war in Iraq costs roughly $7 billion to $8 billion per month, and a postwar occupation could cost $1 billion to $4 billion per month.
So the nature of the occupation -- short and smooth, or long and bumpy -- could have even greater economic and political impact than the war itself.
"There were people in the White House who hoped that this [war] would be a panacea, that it would cure the economy and make the president unbeatable," a Republican insider said. "It's not quite working that way. And that makes this period a very delicate one for Bush -- a very delicate stage."
Times staff writer Nick Anderson contributed to this report.