WASHINGTON, 30 December 2003 — Yesterday we saw how American military force could not end the Vietnam War on favorable terms, because it was a political struggle, and we did not have the political tools to prevail. We did not have means that could achieve our ends.

We may face a similar problem in Iraq, where the original stated objective was to topple a brutal dictator and seize his weapons of mass destruction. This time the initial military phase was easy — Saddam Hussein’s army never really fought back. Capturing Saddam himself was harder, but we did it. But the weapons of mass destruction have not been found. If those weapons never turn up, that would eliminate the key advertised purpose of the war.

So a new mission has been declared: To create a democratic Iraq that will be a model for the Arab world, and a rock of political stability in a turbulent neighborhood. This political goal was always implicit, and the authors of the war told us it would be easy. “We will be greeted as liberators,’’ Vice President Dick Cheney said on the eve of war in March. Iraqi exiles would help us quickly establish a new Baghdad regime, many officials promised. The administration did almost no serious planning for this postwar transition.

It had been warned against this cavalier approach. The first President Bush and his National Security Adviser Brent Scowcroft wrote a book together in 1998 that defended their decision not to take Baghdad at the end of the 1991 Gulf War. In a section written by the elder Bush, it said: “Trying to eliminate Saddam, extending the ground war into an occupation of Iraq ... would have incurred incalculable human and political costs. ... The United States could conceivably still be an occupying power in a bitterly hostile land.’’

Today the United States is an occupying power in a divided Iraq whose rivalrous Shiite, Sunni and Kurdish communities eye us nervously. Though we are rushing to establish a government that will allow us to withdraw, so far there is no plan describing the path to that end that is broadly accepted in Iraq. What started as a pristinely military undertaking now has a primarily political objective. But there is no obvious way to achieve that objective. This is just what happened in Vietnam.

In a recent e-mail interview, one of the senior US commanders in Iraq observed that today’s army has many assets not available to commanders in Vietnam. This senior officer, who agreed to be interviewed on the condition that he not be identified, said that nearly all his officers are on their second or third “nation-building’’ mission, having served earlier in Haiti, Bosnia or Kosovo. His division includes experts on water purification and well-digging, troops that train and organize police units, lawyers and doctors who work with Iraqi counterparts, engineers who rebuild schools and roads, and much more. “This is not rocket science,’’ the officer said of civic action operations. “We’ve got phenomenal capability and the capacity to do great work.’’

But won’t success ultimately depend on political factors that his men cannot control? “You are correct,’’ he replied, “that accomplishment of the military mission here is a necessary, but not a sufficient condition for overall success in Iraq.’’ Creating a stable political situation, a legitimate government and so on was not the responsibility of the US military, this officer said, but of “Ambassador (L. Paul) Bremer and the Iraqi Governing Council.’’

If we see that a neat military victory is impossible and the political goal is difficult to reach, then Iraq and Vietnam begin to have more in common. Sometimes the rhymes ring like chimes. For example:

— Official optimism: Johnson told the country again and again how well things were going in Vietnam. So did key members of his administration and commanders in the field. The happy endings they repeatedly promised never materialized.

Cheney’s “welcomed as liberators’’ prediction is one example of the official optimism about Iraq that proved overly optimistic. Another was the projection made by Pentagon planners last May that the United States would need only about 30,000 troops in Iraq by the end of summer. Today we have 132,000 men and women in the country, and another 30,000 next door in Kuwait.

— American isolation on the ground: In Iraq, as they were in Vietnam, most US installations are surrounded by armed guards, concertina wire or high walls. In Vietnam, few Americans spoke Vietnamese. In Iraq, only a handful speak Arabic, and contacts between Iraqis and Americans are surprisingly rare and often strained. When the war in Vietnam was launched, Americans knew little of Vietnam’s history, most critically the centuries of rivalry between Vietnam and China. The complexities of Shiite and Sunni history, compounded by Kurdish issues that transcend the borders of Iraq (because large numbers of Kurds live in Turkey and Iran) have similarly eluded many Americans on the ground in Iraq who are prosecuting the current war.

— American isolation in the world: Robert S. McNamara, Kennedy’s and Johnson’s secretary of defense, said in a recent interview that if the United States had listened to its allies in the 1960s, when all of them cautioned us not to go to war in Vietnam, we could have avoided that disaster. In 2003 Britain joined the war against Iraq, but all our other traditional allies refused. Vietnam became an unpopular war in many parts of the world; Iraq appears even more so.

— The primacy of American political considerations: It’s too early to see this one clearly, but the rhyme is already audible. An antiwar candidate is the frontrunner for the Democratic nomination. The administration is rushing to complete a transfer of power to Iraqis by July — which could take the air of the issue before the Democratic National Convention — though key Iraqi Shiites are resisting the still-coalescing American plan, and its prospects remain uncertain.

Even before war began, the administration was looking for ways to use it politically. The president’s chief political adviser, Karl Rove, said in January 2002 that Americans “trust the Republican Party to do a better job of protecting and strengthening America’s military might and thereby protecting America.’’ The congressional resolution authorizing Bush to go to war was rushed through in October 2002 before the midterm elections. “People are going to want to know, before the elections, where their representatives stand,’’ explained Rep. Tom Davis of Virginia, then chairman of the National Republican Congressional Committee. Political considerations have also seemed to affect the administration’s views on paying for the war — as they affected Johnson’s in the 1960s. For months the Bush White House refused to speculate on costs. It ruled out any tax increase for the war, which already has added a hundred billion dollars or more to the deficit.

Vietnam undermined the US economy, nearly destroyed the US Army and contributed to a generation or more of public cynicism and distrust of government. There are no grounds today for predicting consequences as grave from the war in Iraq. Indeed, a successful outcome, including a new democratic Iraq, remains possible. But the rhymes should give us pause.