WASHINGTON - New tactics favored by U.S. military officers in Iraq borrow heavily from the end of another war that might seem an unlikely source for a winning strategy: Vietnam.

The tactics, an influx of military advisers and a speeded-up handover to indigenous forces followed by a gradual U.S. withdrawal, resemble those in place as the U.S. effort in Vietnam reached its end.

In historical assessments and the American recollection, Vietnam was the unwinnable war. But to many in the armed forces, Vietnam as a war actually was on its way to succeeding when the Nixon administration and Congress, bowing to public impatience, pulled the plug: first withdrawing U.S. combat forces and then blocking funding and supplies to the South Vietnamese army.

If they hadn't, the South Vietnamese army, which had been bolstered by U.S. advisers and a more focused "hearts and minds" campaign in the later stages of the war, could have fended off the communist North, military thinkers have argued.

In their view, progress was undermined by President Nixon's decision to begin withdrawing U.S. troops in 1969 in the face of political pressure at home, despite military objections that the South Vietnamese army was not ready to go it alone. Another key U.S. mistake, they contend, were the deep cuts by Congress in military aid to Saigon beginning in 1974.

For many in the military, the lesson of Vietnam is clear: Maintain public support and be patient.

Consciously or not, President Bush encapsulated that view during his weekend trip to Hanoi, where he was asked whether there were lessons in Vietnam for the war in Iraq. Instead of military tactics or strategy, he answered by talking about the impatience of the American public, and how success in war can be slow.

"We'll succeed unless we quit," Bush said.

The view that Vietnam could have been won if public opinion and political will had continued to support the war effort is far from universal, particularly among historians outside the military.

Stanley Karnow, a Pulitzer Prize-winning journalist who covered the war from the day the first American was killed in 1959 to its ultimate end, said Hanoi was nowhere near capitulation by 1973 when the Paris Peace Accords were signed.

"They're clutching at some sort of way to justify hanging on in Iraq," said Karnow, whose Vietnam: A History is frequently considered the definitive account of the conflict.

"The war in Vietnam, in my estimation, was unwinnable for the simple, basic reason that we were up against an enemy that was prepared to take on unlimited losses. They would have gone on fighting endlessly."

For years, the debate over the end of the Vietnam War occupied students and scholars in the military's academies and war colleges. But with the Pentagon struggling to find answers in Iraq, the lessons of Vietnam have taken on more than an academic interest.

The course that senior military officers now appear to be steering in Iraq mirrors the "Vietnamization" program implemented by Nixon and his military chief in Vietnam, Army Gen. Creighton Abrams, in the late stages of the war.

Army Gen. John Abizaid, leader of all U.S. forces in the Middle East, laid out that path at congressional hearings last week. He said the biggest change he anticipates in the coming months is a large-scale increase in U.S. advisers.

He also said he hopes to hand over responsibility for security to Iraqi forces in less than a year - faster than Army Gen. George Casey, the U.S. top officer in Iraq, had estimated just weeks earlier - and spelled out his resistance to an increase in American combat troops.

"I believe that more American forces prevent the Iraqis from doing more," Abizaid told the Senate Armed Services Committee. "If more troops need to come in, they need to come in to make the Iraqi army stronger."

For some military experts and historians, several of whom advise the Pentagon on Iraq policy, that strategy sounded familiar, recalling Abrams' shift in Vietnam after taking over from Army Gen. William Westmoreland in 1968.

After that revamp, an increased advisory effort and accelerated pacification program, which included enlarging the South Vietnamese army, was finally beginning to work by the early 1970s, military scholars argue.

Those efforts were undermined, their thesis goes, by a lack of political will at home, which forced South Vietnam to go it alone too soon.