Even as the Bush administration tries to assure Americans that the war in Iraq can still be won, a question hovers in the air like a ghost, even if it is not being explicitly debated: Is Iraq another Vietnam — a war the U.S. is doomed to lose?

The occupation’s defenders reject the parallel between Iraq and Vietnam. But as a historian of the Vietnam War, I find the comparison of the two occupations very revealing. Comparing the two situations leads me to the sobering conclusion that the chances of a foreign occupation succeeding in Iraq are much less than they were in South Vietnam.

The most fundamental factor in this comparison of the two wars is the attitude of the population toward the U.S. occupying forces. In South Vietnam, the anti-Communist regime had already been in power for a full decade by the time the U.S. occupation began. The urban population in most of the cities was accustomed to it and at least tolerated the U.S. occupation, even if they didn’t support it.

In Iraq, the U.S. occupation, having overthrown the Saddam regime, might have been acceptable to most Iraqis if it had not begun blindly and indiscriminately arresting and mistreating tens of thousands of their compatriots — few of whom were involved with the insurgency — in and around the country’s urban areas.

By late March 2004, a USA Today-CNN-Gallup survey of Iraqis found that the support for an immediate U.S. pullout had increased to 57 percent, with only 36 percent saying the United States should “stay longer.” In April, a survey commissioned by the Coalition Provisional Authority itself showed that 82 percent of the respondents disapproved of U.S. and allied forces occupying Iraq.

The Bush administration is betting that national elections in Iraq will somehow change that rejectionist attitude. But it is worth remembering that national elections at a similar point in the war in South Vietnam didn’t make the slightest difference in the attitudes of those whom the United States sought to win over. Even Iraq’s Shiite majority, which has been just as opposed to the continuation of the occupation as the Sunnis, want any elected government to demand U.S. withdrawal.

The hostility toward the occupation in the major cities of Iraq has profound implications for the nature of the war. The fighting in Vietnam took place almost entirely in the countryside. The U.S. was able to bring the full destructive force of its air power to bear on the rural areas controlled by communists and could force most of the civilian population to head for the cities, where the U.S. and the Saigon government had control.

In Iraq, United States forces have no such secure rear area in the cities, especially in the Sunni triangle. It was able to regain control over Fallujah last November only after the city had been emptied of 80 percent of its population — not a tactic that can be repeated in the other cities of Iraq.

Just as was the case in Vietnam, the U.S. command in Iraq acknowledges that the U.S. can only win if Iraqi troops are prepared to rapidly take on an ever-increasing share of the counterinsurgency war. But there the similarity ends.

By 1972, after three years of Vietnamization, the South Vietnamese army had more than a million men under arms and had taken over almost all of the ground combat from the Americans. In contrast, more than a year after the “Iraqization” of the war began, there is not even a shadow of an Iraqi counterinsurgency force.

The reason is simple. Shiites and Sunnis alike refused to fight fellow Iraqis. In every battle to which Iraqi units were sent last year the overwhelming majority of Sunni and Shiite troops either mutinied or deserted, often joining the insurgents. The only indigenous troops willing to fight with the Americans against insurgents have been Kurdish militiamen, whose presence in those Arab cities is highly provocative, given already tense relations between Arabs and Kurds.

The Bush administration is trying to convince the public that Iraq’s troops simply need more training. Yet the adamant refusal of Iraqis to fight the insurgents on behalf of a foreign occupying army is the best evidence of all that Iraq is a far more hopeless mission than Vietnam ever was.