Until recently, the Bush administration has led Americans to believe that war with Iraq can be quick and relatively easy. After all, the 1991 ground war against Iraq lasted only 100 hours. And the campaign in Afghanistan routed the Taliban and al-Qaida in short order (although both survived and still cause big trouble). Both invasions were quickly finished, with few American casualties.

Suddenly, as Gulf War II seems to be only a few weeks away, the administration is putting out a flood of speculation about the hazards of the likely new conflict. It turns out that Secretary of Defense Donald Rumsfeld keeps in his desk drawer a list of things that can go wrong. High on his list is concern that Saddam Hussein may use germ or chemical weapons against his own people and then blame the United States. He worries, too, that Saddam may blow up his oil fields, as he did in Kuwait, to wipe out the future oil revenues that are counted on to help pay for the post-war rebuilding of Iraq.

The worst of this deluge of downside dangers is the possibility of a long, expensive and deadly conflict like the U.S. war in Vietnam, which finally ended in political disaster. Americans have no stomach for protracted warfare and surely would turn against a president who had led the way.

Leaked information about the U.S. plan of attack involves several days of bombing and rocket attacks to destroy Iraqi defenses and control centers, then a rapid ground invasion with the hope of promptly overthrowing Saddam’s government. A U.S. military government would take charge to run the country and feed and shelter the population for perhaps two years while a civilian Iraqi government took shape.

U.S. intelligence has pieced together Saddam’s defense plan. It calls for slowing the American advance by blowing up dams and bridges, igniting the oil fields, and perhaps denying food to Iraqi civilians to confront the invaders with a huge task of caring for desperate millions of people. As the advancing forces approached Baghdad, they would confront defensive rings manned by Republican Guard forces and supplied by stockpiled weapons and ammunition. Some of the Iraqi forces are equipped with special protective gear, an indication that Saddam plans to use poison gas or germ weapons against the American and allied troops. Saddam’s end game is expected to be street-by-street and house-by-house urban warfare, where sophisticated American weapons would lose their advantage and civilian casualties could inflame the Arab world.

Administration officials have said little about the possibility that Saddam may counter with a terror strike against Washington or New York. If an invasion succeeds, that would be Saddam’s “best parting shot,” writes Richard K. Betts in the current Foreign Affairs magazine.

“The United States is about to poke a snake out of fear that the snake might strike sometime in the future, while virtually ignoring the danger that it may strike back when America pokes it.” Mr. Betts, director of the Institute of War and Peace Studies at Columbia University, concedes that Saddam may not be smart enough to figure how to smuggle germ weapons into the United States and set them off. He admits that the odds are low – “perhaps as low as the odds were on Sept. 10, 2001, that 19 Arab civilians would level the World Trade Center and tear a chunk out of the Pentagon.” But he calls it “reckless to bank on maybes” and notes that Saddam has had plenty of time to concoct retaliation, since “the Bush administration has made this war the most telegraphed punch in military history.”

Why is the administration painting a worst-case scenario now? It must recognize that, as the old military saying goes, no battle plan survives the first contact with the enemy. So it makes political sense to warn the American people. If things turn out badly, the government doesn’t want to be accused of relying on a best-case scenario. Whatever the reason, Americans are learning more about the potential consequences of war and cannot say they haven’t been warned.