On the streets of Baghdad today, Americans do not feel welcome. United States military personnel in the city are hunkered down behind acres of fencing and razor wire inside what was once Saddam Hussein's Republican Palace. When L. Paul Bremer III, head of the Coalition Provisional Authority, leaves the compound, he is always surrounded by bodyguards, carbines at the ready, and G.I.'s on patrol in the city's streets never let their hands stray far from the triggers of their machine guns or M-16 rifles. The official line from the White House and the Pentagon is that things in Baghdad and throughout Iraq are improving. But an average of 35 attacks are mounted each day on American forces inside Iraq by armed resisters of one kind or another, whom American commanders concede are operating with greater and greater sophistication. In the back streets of Sadr City, the impoverished Baghdad suburb where almost two million Shiites live -- and where Bush administration officials and Iraqi exiles once imagined American troops would be welcomed with sweets and flowers -- the mood, when I visited in September, was angry and resentful. In October, the 24-member American-appointed Iraqi Governing Council warned of a deteriorating security situation.

Historically, it is rare that a warm welcome is extended to an occupying military force for very long, unless, that is, the postwar goes very smoothly. And in Iraq, the postwar occupation has not gone smoothly.

I have made two trips to Iraq since the end of the war and interviewed dozens of sources in Iraq and in the United States who were involved in the planning and execution of the war and its aftermath. It is becoming painfully clear that the American plan (if it can even be dignified with the name) for dealing with postwar Iraq was flawed in its conception and ineptly carried out. At the very least, the bulk of the evidence suggests that what was probably bound to be a difficult aftermath to the war was made far more difficult by blinkered vision and overoptimistic assumptions on the part of the war's greatest partisans within the Bush administration. The lack of security and order on the ground in Iraq today is in large measure a result of decisions made and not made in Washington before the war started, and of the specific approaches toward coping with postwar Iraq undertaken by American civilian officials and military commanders in the immediate aftermath of the war.

Despite administration claims, it is simply not true that no one could have predicted the chaos that ensued after the fall of Saddam Hussein. In fact, many officials in the United States, both military and civilian, as well as many Iraqi exiles, predicted quite accurately the perilous state of things that exists in Iraq today. There was ample warning, both on the basis of the specifics of Iraq and the precedent of other postwar deployments -- in Panama, Kosovo and elsewhere -- that the situation in postwar Iraq was going to be difficult and might become unmanageable. What went wrong was not that no one could know or that no one spoke out. What went wrong is that the voices of Iraq experts, of the State Department almost in its entirety and, indeed, of important segments of the uniformed military were ignored. As much as the invasion of Iraq and the rout of Saddam Hussein and his army was a triumph of planning and implementation, the mess that is postwar Iraq is a failure of planning and implementation.

1. Getting In Too Deep With Chalabi

In the minds of the top officials of the Department of Defense during the run-up to the war, Iraq by the end of this year would have enough oil flowing to help pay for the country's reconstruction, a constitution nearly written and set for ratification and, perhaps most important, a popular new leader who shared America's vision not only for Iraq's future but also for the Middle East's.

Ahmad Chalabi may on the face of it seem an odd figure to count on to unify and lead a fractious postwar nation that had endured decades of tyrannical rule. His background is in mathematics and banking, he is a secular Shiite Muslim and he had not been in Baghdad since the late 1950's. But in the early 90's he became close to Richard Perle, who was an assistant secretary of defense in the Reagan administration, and in 1992, in the wake of the first gulf war, he founded the Iraqi National Congress, an umbrella organization of Iraqi opposition groups in exile.

In the mid-90's, Chalabi attended conferences on a post-Hussein Iraq organized by Perle and sponsored by the American Enterprise Institute. There he met a group of neoconservative and conservative intellectuals who had served in the administrations of Ronald Reagan and George H.W. Bush, including Dick Cheney, Donald Rumsfeld and Paul Wolfowitz, who later formed the core group that would persuade President George W. Bush to go to war with Iraq. As a number of Iraqi exiles have since related, Wolfowitz, then the dean of the Nitze School of Advanced International Studies at Johns Hopkins University, was particularly appalled and shamed by the first Bush administration's failure to help the Kurds and the southern Shiites in the aftermath of the first gulf war. Encouraged by President Bush to ''take matters into their own hands,'' these groups had risen against Saddam Hussein, only to be crushed by his forces while America did nothing. Wolfowitz and his colleagues believed that removing Saddam Hussein would have been the right way to end the first gulf war, and during their years out of power they lobbied the Clinton administration both publicly and privately to make the overthrow of Saddam Hussein a priority.