WASHINGTON - President Bush drew broad and stinging comparisons Wednesday between the bloodletting and regional chaos that followed the U.S. withdrawal from Vietnam and what could befall the Middle East if American forces leave Iraq "without getting the job done."

"One unmistakable legacy of Vietnam is that the price of America's withdrawal was paid by millions of innocent citizens, whose agony would add to our vocabulary new terms, like 'boat people,' 're-education camps' and 'killing fields,' " Bush said in a speech before the Veterans of Foreign Wars convention in Kansas City, Mo.

Similarly, in Iraq, "to withdraw without getting the job done would be devastating," said Bush, adding that, "Unlike in Vietnam, if we were to withdraw before the job was done, this enemy would follow us home."

For more than four years, Bush has aggressively resisted comparisons between the fighting in Iraq and the Vietnam War, with its unsavory connotations of American quagmire, failure and defeat.

Wednesday marked a dramatic about-face, just weeks before a critical Iraq war update is due to Congress. Bush cited the regional killings and refugee crises that followed the U.S. retreat from Vietnam as a grim historical preview of what could unfold in Iraq if American forces pack up and leave on the kind of deadline some of his political opponents have endorsed.

Analysts and historians fired back, however, saying Bush was rewriting history, or at least drawing the wrong lessons from the war that split the nation a generation ago and took the lives of 58,000 American troops.

"I do not have the same memory as President Bush," said retired Army Gen. John Johns, a Vietnam veteran who spent 12 years specializing in counterinsurgency missions. "What I learned in Vietnam is that U.S. combat forces could not effectively conduct counterinsurgency operations. The longer we stay there, the worse it's going to get."

Others said Bush turned history upside down in suggesting that the pullout from Vietnam helped precipitate genocide in neighboring Cambodia, where an estimated 1.7 million people were killed or starved to death under the communist-backed Khmer Rouge regime headed by Pol Pot.

"It is undoubtedly true that America's failure in Vietnam led to catastrophic consequences in the region, especially in Cambodia," said David C. Hendrickson, a specialist on the history of American foreign policy at Colorado College.

"But there are a couple of further points that need weighing," he told The New York Times. "One is that the Khmer Rouge would never have come to power in the absence of the war in Vietnam -- this dark force arose out of the circumstances of the war, was in a deep sense created by the war. The same thing has happened in the Middle East today. Foreign occupation of Iraq has created far more terrorists than it has deterred."

Cambodia's chaos

In the years before Pol Pot's 1975 rise to power, U.S. forces bombed Cambodia and ran secret ground incursions, ostensibly to go after North Vietnamese forces who were taking refuge in that country and using it to stage attacks against Americans in neighboring Vietnam.

The result -- open war between a U.S.-backed government in Cambodia and insurgents backed by North Vietnam -- destabilized Cambodia "and opened the door to Pol Pot and the genocide that was carried out by his followers and the Khmer Rouge," said Steven Simon, senior fellow for Middle Eastern studies with the Council on Foreign Relations. "These things happened because the United States left too late, not because the U.S. left too early."

Not all historians accept that explanation. Some have sided with Bush, saying it was the withdrawal of American combat forces from Vietnam -- most were out by 1973 -- that gave Hanoi the ability to buttress the Khmer Rouge guerrillas that toppled the government in Cambodia.

Simon said, though, that if there is a comparison to be made between Vietnam and Iraq, it's a cautionary tale, illustrating the perils of using military force to try to engineer good governance abroad.

"We never had a government in Saigon that had the respect, loyalty and legitimacy accorded to it by the South Vietnamese people," said Simon, who directed global policy for the White House National Security Council during the Clinton administration.

Likewise in Iraq, he said, military operations alone can't win the day.

"You need Iraqi politicians who can take advantage of increased security, that will pursue a policy of national reconciliation that will put an end to this civil war," Simon said. "But there is no such government."

Worries about Maliki

Wednesday's speech was part of a broader White House campaign aimed at bolstering sagging public support for the Iraq war in advance of a critical progress report to be delivered to Congress in mid-September by Gen. David Petraeus, the overall commander of U.S. forces in Iraq.

It also came amid rising concerns in Washington over the performance of Iraqi Prime Minister Nouri al-Maliki, who has made little progress toward bridging the sectarian divide in his country, The New York Times reported.

On Wednesday, as a second Democratic senator, Hillary Rodham Clinton of New York, called for Maliki to quit, the Iraqi prime minister lashed out at American lawmakers who have questioned his competence.

Maliki, on a trip to Syria, said that no one has the right to impose timetables on his elected government and that Iraq can "find friends elsewhere." Without naming any American official, Maliki said some criticism of him and his government in recent days had been "discourteous," The Associated Press reported.

Bush -- who on Tuesday confessed to "a certain level of frustration" with the Iraqi government -- responded by using Wednesday's speech to try to shore up Maliki. "Prime Minister Maliki is a good guy, a good man with a difficult job," he told the veterans, "and I support him."

On Monday, Senate Armed Services Committee Chairman Carl Levin, D-Mich., urged Iraq's Parliament to oust Maliki.

Bush's speech drew criticism from Senate Majority Leader Harry Reid, D-Nev., who pledged to seek legislative ways to force a change in course in Iraq when Congress returns from its August recess after Labor Day.

"Instead of providing the country with a history lesson, the president should be re-evaluating his flawed strategies that have led to one of the worst foreign policy blunders in our nation's history," Reid said in a statement.

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